feat: add JSObject constructors

[DonIsaac]

What does this PR do?

• Add constructors to JSObject for marshalling structs
• Refactor some existing code to use them

How did you verify your code works?

Code change affects existing code; I ran the tests.

[robobun]

❌ @DonIsaac, your commit eed2b01 has 10 failures in #7929:

test/js/bun/http/serve.test.ts - 2 failing on 🍎 14 x64

test/js/bun/http/serve.test.ts - 2 failing on 🍎 13 x64

test/regression/issue/ctrl-c.test.ts - 1 failing on 🐧 22.04 x64

test/cli/install/registry/bun-install-registry.test.ts - timeout on 🐧 24.04 aarch64

test/cli/install/registry/bun-install-registry.test.ts - timeout on 🐧 22.04 x64-baseline

test/v8/v8.test.ts - 22 failing on 🐧 3.20 aarch64

test/v8/v8.test.ts - 22 failing on 🐧 3.20 x64-baseline

test/v8/v8.test.ts - 22 failing on 🐧 3.20 x64

test/js/bun/css/doesnt_crash.test.ts - 1 failing on 🐧 3.20 aarch64

test/cli/run/require-cache.test.ts - 1 failing on 🐧 12 aarch64

test/cli/run/require-cache.test.ts - 1 failing on 🐧 22.04 aarch64

test/cli/run/require-cache.test.ts - 1 failing on 🐧 3.20 aarch64

test/cli/run/require-cache.test.ts - 1 failing on 🐧 3.20 x64

test/cli/run/require-cache.test.ts - 1 failing on 🍎 14 x64

test/cli/run/require-cache.test.ts - 1 failing on 🍎 13 x64

test/js/node/dns/node-dns.test.js - 1 failing on 🪟 2019 x64-baseline

test/js/bun/http/serve-body-leak.test.ts - 1 failing on 🪟 2019 x64-baseline

test/integration/next-pages/test/dev-server-ssr-100.test.ts - 1 failing on 🪟 2019 x64

test/integration/next-pages/test/dev-server-ssr-100.test.ts - 1 failing on 🪟 2019 x64-baseline

test/integration/next-pages/test/next-build.test.ts - 1 failing on 🍎 13 aarch64

test/integration/next-pages/test/next-build.test.ts - 1 failing on 🍎 14 aarch64

[DonIsaac]

Prereq for #15698

[paperdave]

realizing this means createEmptyObject(0) -> JSObject.create(.{})

i'll write documentation for $bindgenFn