Port #62483: Disable conditional exports fallbacks on null values

[Copilot]

Ports microsoft/TypeScript#62483.

When a package.json conditional export maps a specifier to null, the resolver was treating it as "not found, keep searching," allowing fallback to subsequent conditions like types. Per Node.js semantics, null should terminate resolution for that entry.

{
  "exports": {
    ".": {
      "import": null,
      "types": "./dist/index.d.ts"
    }
  }
}

Previously, import: null would fall through to types, incorrectly resolving the module. Now it correctly stops resolution.

• Changed the JSONValueTypeNull case in loadModuleFromTargetExportOrImport from continueSearching() to unresolved() — stops the search instead of falling through
• Added result.isResolved() guard on the "Resolved under condition" trace — a null match shouldn't be traced as a resolution

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[Copilot]

Pull request overview

Ports TypeScript #62483 to align package.json conditional exports resolution with Node.js semantics: when an exports/imports target is null, resolution should terminate for that entry (no fallback to later conditions like types).

Changes:

• Treat JSONValueTypeNull targets as terminal-unresolved (unresolved()) instead of “keep searching” (continueSearching()).
• Only emit the “Resolved under condition …” trace when the result is actually resolved.
• Update conformance baselines to reflect that null blocks fallback and the module is not resolved.

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
internal/module/resolver.go	Stops conditional exports resolution when a matched condition maps to null; prevents misleading “resolved” tracing for unresolved results.
testdata/baselines/reference/submodule/conformance/conditionalExportsResolutionFallbackNull(moduleresolution=nodenext).trace.json	Updates trace to show resolution terminates on null and the module is not resolved.
testdata/baselines/reference/submodule/conformance/conditionalExportsResolutionFallbackNull(moduleresolution=nodenext).errors.txt	Updates expected diagnostics to include the unresolved module error (TS2307).
testdata/baselines/reference/submodule/conformance/conditionalExportsResolutionFallbackNull(moduleresolution=nodenext).errors.txt.diff	Removes outdated diff baseline content (no longer applicable).
testdata/baselines/reference/submodule/conformance/conditionalExportsResolutionFallbackNull(moduleresolution=node16).trace.json	Same baseline update for node16 resolution mode.
testdata/baselines/reference/submodule/conformance/conditionalExportsResolutionFallbackNull(moduleresolution=node16).errors.txt	Same expected diagnostic update for node16 resolution mode.
testdata/baselines/reference/submodule/conformance/conditionalExportsResolutionFallbackNull(moduleresolution=node16).errors.txt.diff	Removes outdated diff baseline content (no longer applicable).
testdata/baselines/reference/submodule/conformance/conditionalExportsResolutionFallbackNull(moduleresolution=bundler).trace.json	Same baseline update for bundler resolution mode.
testdata/baselines/reference/submodule/conformance/conditionalExportsResolutionFallbackNull(moduleresolution=bundler).errors.txt	Adds expected TS2307 diagnostic baseline for bundler mode output.
testdata/baselines/reference/submodule/conformance/conditionalExportsResolutionFallbackNull(moduleresolution=bundler).errors.txt.diff	Removes outdated diff baseline content (no longer applicable).