lang: Fix constant bytes declarations when using declare_program!

[acheroncrypto]

Problem

Declaring a bytes constant:

#[constant]
pub const MY_CONST: &[u8] = &[1, 2, 3, 4];

generates the following constants section in the IDL:

"constants": [
    {
      "name": "MY_BYTES",
      "type": "bytes",
      "value": "[1, 2, 3, 4]"
    }
]

Using this IDL with declare_program! panics with:

error: proc macro panicked
 --> programs/my-program/src/lib.rs:9:1
  |
9 | declare_program!(some_program);
  | ^^^^^^^^^^^^^^^^^^^^^
  |
  = help: message: called `Result::unwrap()` on an `Err` value: Error("unexpected end of input, expected expression")

Initially reported in the Anchor Discord server.

Summary of changes

Fix constant bytes declarations when using declare_program! by handling constants that have the type IdlType::Bytes separately.

[vercel]

@acheroncrypto is attempting to deploy a commit to the coral-xyz Team on Vercel.

A member of the Team first needs to authorize it.