Formal spec text tracking

[eqrion]

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

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

cc @ajklein who was interested in this.

[eqrion]

I think we've just about got all of this now.