Deprecate import assert in favor of import with

[jakebailey]

Fixes #62210

I updated all tests to with, then introduced two tests just for assert, deprecated and not.

[Copilot]

Pull request overview

This pull request deprecates the use of assert keyword in favor of with for import attributes, aligning TypeScript with the updated JavaScript standard. The PR updates all existing tests to use with and adds two new test files to verify the deprecation behavior.

Changes:

• Source code change adds deprecation warning for assert keyword
• Conversion of 30+ test files from assert to with syntax
• Two new test files: one for deprecation errors, one for ignored deprecation

Reviewed changes

Copilot reviewed 139 out of 139 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/compiler/checker.ts	Adds deprecation logic for assert keyword
tests/cases/compiler/importAssertionsDeprecated.ts	New test for deprecation error
tests/cases/compiler/importAssertionsDeprecatedIgnored.ts	New test with ignoreDeprecations flag
tests/cases/fourslash/*.ts	Convert fourslash tests from assert to with
tests/cases/conformance/**/*.ts	Convert conformance tests from assert to with
tests/baselines/reference/**/.	Updated baselines reflecting error message changes