[dart2wasm] Umbrella issue for dart2wasm work

[mkustermann]

Important for adoption & customers:

• [dart2wasm] Add dart2wasm --dry-run option #60050
• [dart2wasm] Help to deal with minified errors from deployed apps #60711
• [dart2wasm] Follow-up tasks on source maps #56232

=> Unblock production apps (e.g. DevTools)
=> Unblocking flutter to auto-enable wasm or at least tell users to enable wasm if possible.

Finishing remaining bugs / features:

• [dart2wasm] Go over approved failures in all configurations and get to a 0 approved failures (modulo e.g. CFE issues and experimental co19 tests) #60933

=> We're deploying by default in -O2 mode and have to have better testing of that mode (which includes --minify)

JS Interop issues

• [dart2wasm] make dart.library.js_util false on conditional imports #56502
• JS Interop types have .hashCode == 0 #55823
• [dart2wasm] JS errors can't be caught using an interop type #55481
• allowInterop is leaking closure instances via global map #54908
• dartify doesn't convert Promises on dart2wasm #54573
• [dart2wasm/dart:js_interop] Invalid conversions between primitive JS types do not throw #54179

Infrastructure

• [dart2wasm] Better infrastructure/tooling to debug where binary size is coming from #60929
• [dart2wasm] Better testing of size/perf optimizations #60928

Optimizations (perf/size):

• [dart2wasm] Revisit binaryen flags we use when compiling apps #60931
• [dart2wasm] Experiment with using tagged integers instead of boxing all integers #60930
• Unboxing
  [dart2wasm] Consider treating JSValue a primitive type and unbox it in fields & function signatures #60455
  [dart2wasm] Unbox record return values in dart2wasm if beneficial #56611
  Unboxing of SIMD typed data

=> Ensure dart2wasm is on par or better than dart2js and other languages

Wasm & FFI Interop

• [ffi/js-interop/wasm] Unified API for using dart:ffi and JS Interop with WASM #46690
• Allow dart2wasm to interop with other wasm code & provide wasm data structures (e.g. in dart:wasm) #55856, Provide interop between Dart and WASM #37355

WasmGC Spec

• [dart2wasm/spec-proposal] Experiment with "custom descriptors" / custom RTTs #60932
• [dart2wasm/spec-proposal] Experiment "Shared-Everything Threads Proposal" proposal with possible usage for isolates on the web #55364
• [dart2wasm/spec-proposal] Experiment with "Stack-switching" proposal #60942

/cc @mraleph