Add esnext transform

[rbuckton]

This adds the ESNext transform, which handles the downlevel transformation of using and await using declarations.

This PR is dependent on #815, so most feedback related to ast/ast.go, printer/emitcontext.go, and printer/factory.go should be addressed there.

[Copilot]

Pull Request Overview

This PR adds support for the ESNext transform to downlevel ‘using’ and ‘await using’ declarations by modifying the transformation and printer layers, among other updates. Key changes include renaming module IIFE parameters in baseline tests, updating various helper and AST transformation functions from binary expressions to assignment expressions, and revising name generation and helper functions in the printer.

Reviewed Changes

Copilot reviewed 460 out of 461 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
testdata/baselines/reference/submodule/compiler/collisionCodeGenModuleWithConstructorChildren.js	Renames IIFE parameter from M_1 to M_2 to avoid conflicts
testdata/baselines/reference/submodule/compiler/collisionCodeGenModuleWithAccessorChildren.js	Consistent renaming of IIFE parameters to M_2 and M_3
internal/transformers/*.go	Updates transformation logic (e.g. replacing NewBinaryExpression with NewAssignmentExpression) to support ESNext syntax
internal/printer/*	Adjustments in name generation and helper invocations including updates in test expectations
internal/ast/utilities.go	Added a new helper (RangeIsSynthesized) for synthetic position checking

Files not reviewed (1)

• testdata/baselines/reference/submodule/compiler/collisionCodeGenModuleWithAccessorChildren.js.diff: Language not supported

Comments suppressed due to low confidence (2)

internal/printer/namegenerator_test.go:208

• [nitpick] The test currently expects "foo_2" for a unique name in a scoped context, although the comment indicates that "foo_1" may be more appropriate. Please verify and update the expected behavior in line with the intended scoping rules once the port is complete.

assert.Equal(t, "foo_2", g.GenerateName(name2)) // Matches Strada, but is incorrect

internal/printer/namegenerator.go:106

• [nitpick] This comment indicates that the generated names are currently being added to a global set rather than being scoped per the current nameGenerationScope. Consider revising this logic so that generated names are tracked per scope if that behavior is the intended design.

g.generatedNames.Add(name) // NOTE: Matches Strada, but is incorrect.