Add regression test for JSX runtime resolution in scripts

[GermanoB (germanao)]

Summary

• Add a compiler regression case for JSX in a script with jsxImportSource pointing to an installed runtime package.
• Cover the matching file with export {} and verify both resolve JSX.Element from the runtime.
• Cover the current compiler behavior, which avoids the misleading TS2875 and TS7026 diagnostics reported in Incorrect/unhelpful error message for non-module jsx file #64438. The case still reproduces those diagnostics with TypeScript 6.0.3.

Related to #64438. This PR adds regression coverage; it does not change compiler behavior or the wording of those diagnostics in TypeScript 6.0.3.

Validation

• go -C ./tsc test -run 'TestLocal/jsxRuntimeScriptDiagnostic' ./internal/testrunner — passed.
• npx hereby check:format — passed.

AI assistance

This PR was authored with Codex AI assistance. I will review the patch and handle maintainer feedback.

[typescript-automation]

This PR doesn't have any linked issues. Please open an issue that references this PR. From there we can discuss and prioritise.

[Copilot]

Copilot review overview

🟢 Approval recommended

The focused regression test and generated baselines consistently validate the intended behavior.

Review effort: Balanced
Findings: None

What changed in this PR

Adds regression coverage for JSX runtime resolution in script and module files.

Changes:

• Adds a NodeNext JSX runtime fixture.
• Confirms runtime JSX.Element and intrinsic symbol resolution.
• Records expected type, symbol, and emit baselines.

File	Description
jsxRuntimeScriptDiagnostic.tsx	Defines the regression scenario.
jsxRuntimeScriptDiagnostic.types	Verifies inferred JSX types.
jsxRuntimeScriptDiagnostic.symbols	Verifies intrinsic symbol resolution.
jsxRuntimeScriptDiagnostic.js	Records expected emit.

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[GermanoB (germanao)]

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