proc config function should be able to index non-channel type

[proppy]

Describe the bug
It seems that proc's config function assuming that all indexing is done against channel types.

To Reproduce
ir_convert on the following code:

const F32_0 = float32::zero(false);
const F32_2 = F32 { sign: false, bexp: u8:128, fraction: u23:0 };
const WEIGHTS = F32[u32:4][u32:4]:[
    [F32_2, F32_0, F32_0, F32_0], [F32_0, F32_2, F32_0, F32_0], [F32_0, F32_0, F32_2, F32_0],
    [F32_0, F32_0, F32_0, F32_2],
];

proc matmul<ROWS: u32, COLS: u32> {
    south_outputs: chan<F32>[COLS][ROWS] out;
    west_inputs: chan<F32>[COLS][ROWS] in;

    config(activations_in: chan<F32>[ROWS] in, results_out: chan<F32>[COLS] out) {
        let (east_outputs, west_inputs) = chan<F32>[COLS][ROWS]("east_west");

        let (south_outputs, north_inputs) = chan<F32>[COLS][ROWS]("north_south");

        spawn node(
            activations_in[0], north_inputs[0][0], east_outputs[0][0], south_outputs[1][0],
            WEIGHTS[0][0]);
        spawn node(
            west_inputs[0][0], north_inputs[0][1], east_outputs[0][1], south_outputs[1][1],
            WEIGHTS[0][1]);
        spawn node(
            west_inputs[0][1], north_inputs[0][2], east_outputs[0][2], south_outputs[1][2],
            WEIGHTS[0][2]);
        spawn node(
            west_inputs[0][2], north_inputs[0][3], east_outputs[0][3], south_outputs[1][3],
            WEIGHTS[0][3]);

        spawn node(
            activations_in[1], north_inputs[1][0], east_outputs[1][0], south_outputs[2][0],
            WEIGHTS[1][0]);
        spawn node(
            west_inputs[1][0], north_inputs[1][1], east_outputs[1][1], south_outputs[2][1],
            WEIGHTS[1][1]);
        spawn node(
            west_inputs[1][1], north_inputs[1][2], east_outputs[1][2], south_outputs[2][2],
            WEIGHTS[1][2]);
        spawn node(
            west_inputs[1][2], north_inputs[1][3], east_outputs[1][3], south_outputs[2][3],
            WEIGHTS[1][3]);

        spawn node(
            activations_in[2], north_inputs[2][0], east_outputs[2][0], south_outputs[3][0],
            WEIGHTS[2][0]);
        spawn node(
            west_inputs[2][0], north_inputs[2][1], east_outputs[2][1], south_outputs[3][1],
            WEIGHTS[2][1]);
        spawn node(
            west_inputs[2][1], north_inputs[2][2], east_outputs[2][2], south_outputs[3][2],
            WEIGHTS[2][2]);
        spawn node(
            west_inputs[2][2], north_inputs[2][3], east_outputs[2][3], south_outputs[3][3],
            WEIGHTS[2][3]);

        spawn node(
            activations_in[3], north_inputs[3][0], east_outputs[3][0], results_out[0], WEIGHTS[3][0]);
        spawn node(
            west_inputs[3][0], north_inputs[3][1], east_outputs[3][1], results_out[1], WEIGHTS[3][1]);
        spawn node(
            west_inputs[3][1], north_inputs[3][2], east_outputs[3][2], results_out[2], WEIGHTS[3][2]);
        spawn node(
            west_inputs[3][2], north_inputs[3][3], east_outputs[3][3], results_out[3], WEIGHTS[3][3]);

        (south_outputs, west_inputs)
    }

    init { () }
    next(state: ()) {
        unroll_for! (col, _): (u32, ()) in u32:0..COLS {
            send(join(), south_outputs[0][col], float32::zero(false));
        }(());
        unroll_for! (row, _): (u32, ()) in u32:0..ROWS {
            recv(join(), west_inputs[row][3]);
        }(());
    }
}

fails with the following error:

xls/dslx/frontend/bindings.cc:55
Error: NOT_FOUND: Not a channel or channel array: WEIGHTS; Failed to convert input to IR for comparison. Consider turning off comparison with `--compare=none`: 
=== Source Location Trace: === 
xls/common/status/status_builder.cc:197
xls/dslx/ir_convert/channel_scope.cc:368
xls/dslx/ir_convert/proc_config_ir_converter.cc:143
xls/dslx/ir_convert/proc_config_ir_converter.cc:260
xls/dslx/ir_convert/proc_config_ir_converter.cc:105
xls/dslx/ir_convert/ir_converter.cc:185
xls/dslx/ir_convert/ir_converter.cc:326
xls/dslx/ir_convert/ir_converter.cc:349
xls/dslx/ir_convert/ir_converter.cc:361
xls/dslx/run_routines/run_routines.cc:719
xls/dslx/interpreter_main.cc:203

Expected behavior

proc can access any array type in config.

[proppy]

related, it seems that we currently throw an out of bound error when attempt to ir convert a proc spawning a child proc w/ a non channel array argument:

import float32;
type F32 = float32::F32;

proc matmul<ROWS: u32, COLS: u32> {
    south_outputs: chan<F32>[COLS][ROWS] out;
    west_inputs: chan<F32>[COLS][ROWS] in;

    config(activations_in: chan<F32>[ROWS] in, results_out: chan<F32>[COLS] out,
           weights: F32[ROWS][COLS]) {
        let (east_outputs, west_inputs) = chan<F32>[COLS][ROWS]("east_west");

        let (south_outputs, north_inputs) = chan<F32>[COLS][ROWS]("north_south");
        (south_outputs, west_inputs)
    }

    init { () }

    next(state: ()) {
      ()
    }
}


const F32_0 = float32::zero(false);
const F32_2 = F32 { sign: false, bexp: u8:128, fraction: u23:0 };
const WEIGHTS = F32[u32:4][u32:4]:[
    [F32_2, F32_0, F32_0, F32_0], [F32_0, F32_2, F32_0, F32_0], [F32_0, F32_0, F32_2, F32_0],
    [F32_0, F32_0, F32_0, F32_2],
];


proc matmul_4x4 {
    config(activations_in: chan<F32>[4] in, results_out: chan<F32>[4] out) {
        spawn matmul<u32:4, u32:4>(activations_in, results_out, WEIGHTS);
    }

    init { () }

    next(state: ()) {  }
}

F1127 23:16:48.470303    6186 throw_delegate.cc:112] RAW: absl::container_internal::raw_hash_map<>::at
absl::raw_log_internal::RawLog()
absl::base_internal::ThrowStdOutOfRange()
xls::dslx::ProcConfigIrConverter::HandleSpawn()
xls::dslx::ProcConfigIrConverter::HandleStatement()
xls::dslx::ProcConfigIrConverter::HandleStatementBlock()
xls::dslx::ProcConfigIrConverter::HandleFunction()
xls::dslx::(anonymous namespace)::ConvertCallGraph()
xls::dslx::ConvertModuleIntoPackage()
xls::dslx::ConvertModuleToPackage()
xls::dslx::AbstractTestRunner::ParseAndTest()
main
__libc_start_main
_start

[proppy]

related, it seems that we currently throw an out of bound error when attempt to ir convert a proc spawning a child proc w/ a non channel array argument:

This seems to be related to the arguments being marked as const.