Formal spec text tracking

This is a tracking issue for updates to the formal text for phase 4.

[x] Merge with upstream wasm3.0 branch to get GC
[x] Add section defining the 'Builtins' concept
[x] Add WebAssemblyCompileOptions to WebIDL and thread through compile/instantiation methods
[x] WebAssembly.Module object gets a slot for an ordered list of builtin groups that are enabled
[x] 'compile a module' algorithm does an eager import matching step against the builtin groups that are enabled
[x] 'instantiate a module' algorithm instantiates builtins into hostfuncs and passes them as imports
[x] WebAssembly.Module.imports() should hide imports that refer to a builtin group
[x] Add definitions for 'wasm:js-string' function builtins
[x] Add 'importedStringConstants' to WebAssemblyCompileOptions, define similarly to builtins?

cc @ajklein who was interested in this.

WebAssembly / js-string-builtins