Split "use strict" into separate transformer, fix bugs with prologues

[jakebailey]

This fixes a massive number of diffs relating to prologues, including missing "use strict" or duplicating prologues/comments in general.

Before, "use strict" was added in the CJS transform. But this meant we were not adding it to non-CJS files that also needed it, e.g. scripts.

This PR splits the functionality out into a fine-grained transform which handles just adding "use strict", drops the code from CJS, then fixes related bugs in transforms/emit that were causing things to break with this fix in place.

After this PR, there are no missing "use strict" in any diffs, except for files which are missing entire files or are in general not being detected as ESM correctly. (only 9 diffs last I checked)

[Copilot]

Pull Request Overview

This pull request refactors how "use strict" directives are emitted by moving the logic from the CommonJS module transformer into a dedicated UseStrictTransformer. This fixes numerous baseline differences where "use strict" was previously missing or being duplicated in various compilation scenarios.

Key Changes

• Created a new UseStrictTransformer that runs before module transformation
• Removed "use strict" emission logic from the CommonJS module transformer
• Fixed prologue splitting to correctly handle cases where all statements are prologue
• Updated printer to emit only non-prologue statements when emitting function bodies

Reviewed Changes

Copilot reviewed 300 out of 1181 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
internal/transformers/estransforms/usestrict.go	New transformer that adds "use strict" based on module type and compiler options
internal/transformers/moduletransforms/commonjsmodule.go	Removed "use strict" logic that now belongs in the dedicated transformer
internal/compiler/emitter.go	Added the new UseStrictTransformer to the transformation pipeline
internal/printer/factory.go	Fixed SplitStandardPrologue to return all statements as prologue when applicable
internal/printer/printer.go	Updated to use emitListRange to skip prologue statements in function bodies
testdata/baselines/reference/**/*.js	Baseline updates showing "use strict" now correctly appears once at the start of files
testdata/baselines/reference/**/*.js.diff	Diff files showing removal of duplicate "use strict" directives

[jakebailey]

@sheetalkamat I don't really know how to handle this one; the test seems to be flaky. It seems to me like we are not correctly noting that strict/alwaysStrict are emit affecting (or even bind affecting!)