Include jsDiagnostics in parser state mark/rewind

[ahejlsberg]

Fixes #1749.

[Copilot]

Pull Request Overview

Fixes speculative parsing in JavaScript files by properly handling JavaScript-specific diagnostics during parser state mark/rewind operations. When the parser marks a state for potential backtracking and later rewinds, it now correctly restores both regular diagnostics and JavaScript-specific diagnostics to their previous state.

• Added jsDiagnosticsLen field to ParserState to track JavaScript diagnostic count
• Modified mark() method to capture current JavaScript diagnostics length
• Updated rewind() method to truncate jsDiagnostics array to the saved length

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
internal/parser/parser.go	Adds JavaScript diagnostics tracking to parser state mark/rewind mechanism
testdata/tests/cases/compiler/jsSpeculativeParsingError.ts	Test case demonstrating the fix for JavaScript speculative parsing errors
testdata/baselines/reference/compiler/jsSpeculativeParsingError.types	Expected type output baseline for the test case
testdata/baselines/reference/compiler/jsSpeculativeParsingError.symbols	Expected symbol output baseline for the test case