Ensure we use the right checker in declaration diagnostics, fix lifetime

[jakebailey]

Propagate the request-scoped checker to declaration diagnostics. This was a TODO, and the main source of races. This involved a bunch of surgery but I think the new code makes sense?

Fixes #1160 (probably)

[Copilot]

Pull Request Overview

Propagate a request-scoped checker into declaration diagnostics and update EmitResolver APIs to remove the file parameter, reducing races.

• Switched GetEmitResolver(file) APIs to GetEmitResolver() and threaded a per-file checker via newEmitHost
• Updated NewDeclarationTransformer to pull its resolver from the host directly
• Adjusted diagnostic and emitter logic to use context-bound hosts

Reviewed Changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
internal/transformers/tstransforms/importelision_test.go	Updated test to call the no-arg GetEmitResolver
internal/transformers/declarations/transform.go	Removed resolver parameter from constructor, fetching via host
internal/printer/emithost.go	Changed EmitHost API to use no-arg GetEmitResolver
internal/compiler/program.go	Rewrote declaration diagnostics to use newEmitHost with context
internal/compiler/emitter.go	Updated emitter methods to drop file arg and add SourceFiles()
internal/compiler/emitHost.go	Introduced newEmitHost, removed old resolver method
internal/checker/symbolaccessibility.go	Cleaned up GetEmitResolver() call
internal/checker/nodebuilderimpl.go	Cleaned up GetEmitResolver() calls
internal/checker/checker.go	Simplified GetEmitResolver() signature

Comments suppressed due to low confidence (1)

internal/compiler/emitHost.go:34

• The EmitHost interface removed its old GetEmitResolver(file) method but does not declare the new zero-argument GetEmitResolver() method. Add GetEmitResolver() printer.EmitResolver to the interface so emitHost satisfies it.

	IsEmitBlocked(file string) bool