Fix parameter property modifier followed by newline (fixes #28396)

[Abhirup0]

Fixes #28396

Summary

When parsing constructor parameter property modifiers (public, private, protected, readonly, override), trailing line breaks between the modifier and parameter name caused nextTokenIsOnSameLineAndCanFollowModifier() to reject the modifier keyword. The parser subsequently fell back to treating the modifier keyword as a parameter name, emitting a syntax error due to a missing comma.

This PR passes permitLineBreak = true when parsing modifiers in parseParameterWorker(), allowing parameter property modifiers followed by a newline to be correctly recognized as modifiers when a valid parameter identifier follows.

Test Plan

• Added tests/cases/compiler/parameterPropertyWithNewline.ts with baselines.
• Ran npx hereby runtests --tests=parameterProperty (54/54 tests passing).
• Ran npx hereby lint (0 errors, 0 warnings).

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Disclosure: Authored, reviewed, and verified by me with AI pair-programming assistance (Antigravity/Gemini).

[Abhirup0]

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[Copilot]

Pull request overview

Fixes a longstanding parser edge case where constructor parameter property modifiers (public/private/protected/readonly/override) were not recognized if a line break appeared before the parameter name, causing the modifier keyword to be mis-parsed as a parameter name.

Changes:

• Extend modifier lookahead to optionally permit line breaks when deciding whether a token is a modifier.
• Enable that behavior when parsing parameter modifiers (parseParameterWorker).
• Add a new compiler test and baselines validating parameter properties with a newline after the modifier.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/compiler/parser.ts	Adds a permitLineBreak path for modifier lookahead and uses it during parameter parsing to recognize parameter property modifiers across newlines.
tests/cases/compiler/parameterPropertyWithNewline.ts	New regression test covering parameter property modifiers split by a newline.
tests/baselines/reference/parameterPropertyWithNewline.types	Baseline for types output of the new regression test.
tests/baselines/reference/parameterPropertyWithNewline.symbols	Baseline for symbols output of the new regression test.
tests/baselines/reference/parameterPropertyWithNewline.js	Baseline for JS emit output of the new regression test.

[MartinJohns]

@Abhirup0 You should read this: https://github.com/microsoft/TypeScript/blob/main/CONTRIBUTING.md#notes-on-contributing

[Abhirup0]

Thanks @MartinJohns ! I have updated the PR description to include the AI assistance disclosure.