Implement component encoding.

[peterhuene]

This giant PR implements encoding of resolved WAC documents, effectively enabling component composition.

Changes to the grammar:

• resource methods no longer accept references to function types (WIT compat).

Changes to the AST:

• The AST printer moved into the ast module.
• Fixed or not printing correctly for printing lookahead failures.
• Fixed segment spans in a package path not being calculated correctly.
• Types now store their span; used in new resolution diagnostics.

Changes to resolution:

• The majority of the resolution logic has been refactored out into an ast submodule.
• A check was added to ensure function result types do not contain a borrow.
• There is now a package arena so that instantiations (and implicit imports) can keep track of the originating package for better diagnostic messages.
• The value type enum was refactored such that borrows and owns of resources don't need allocations in the types arena (unless aliased with type foo = borrow<x>).
• The Item struct and ItemSource enum were merged into a single Item enum.
• Support for aliasing resources was added (e.g. type r2 = r;).
• The Resource type no longer stores a collection of related methods as this greatly complicated merging of implicit imports; now resource methods are exported/imported directly in the exports/imports of an interface/world.
• Consequently, merging of implicitly imported instances is now correctly implemented.
• Subtype checking relating to resources has been improved so that the ResourceMap is no longer required.
• Scope rules now better align with WIT; an interface or world may no longer reference top-level types.
• Decoding binary packages now properly resolves resources and "used" types in interface and world definitions.
• The type cache for binary decoding was removed as it was both overly complex and didn't work properly with resources.

Implementation of encoding:

• Encoding of WIT subset of the grammar should match that of the existing WIT tooling; may be round-tripped with wasm-tools component wit.
• Encoding of imports, instantiations, and exports should enable the output of actual WebAssembly compositions.

CLI changes:

• The parse command has been split into three different commands:

  • The parse command that outputs a JSON formatted AST.
  • The resolve command that outputs a JSON formatted resolved document.
  • The encode command that outputs with text or binary WebAssembly.

[peterhuene]

@fibonacci1729 absolutely no rush on this review; hopefully this is the last huge refactoring review I'll have for a while (🤞).

[fibonacci1729]

Looks great!