fix: ability to handle FDv1 flagValues shorthand map to FDv2FiledataInitializer

[joker23]

Note

Low Risk
Scoped additive change to local file data loading with documented semantic differences from FDv1 and thorough unit tests; no auth or network surface.

Overview
FDv2 file data initialization now accepts the FDv1-style flagValues map ({ flagKey: variationValue }) in JSON/YAML files, converting each entry into a single-variation flag via shared makeFlagWithValue (now exported from FileDataSource).

flagValues are merged with full flags and segments when combining multiple paths; later sources win for the same key (including flags vs flagValues across files). Shorthand-derived flags always use version 1—unlike FDv1 there is no version bump on value change, and duplicates are not rejected.

Coverage adds tests for shorthand-only files, mixed keys in one file, multi-file merge, and cross-file override behavior.

^{Reviewed by Cursor Bugbot for commit 45fadbb. Bugbot is set up for automated code reviews on this repo. Configure here.}

[github-actions]

@launchdarkly/js-sdk-common size report
This is the brotli compressed size of the ESM build.
Compressed size: 26360 bytes
Compressed size limit: 29000
Uncompressed size: 129188 bytes

[github-actions]

@launchdarkly/js-client-sdk size report
This is the brotli compressed size of the ESM build.
Compressed size: 32030 bytes
Compressed size limit: 34000
Uncompressed size: 114438 bytes

[github-actions]

@launchdarkly/js-client-sdk-common size report
This is the brotli compressed size of the ESM build.
Compressed size: 38887 bytes
Compressed size limit: 39000
Uncompressed size: 212703 bytes

[github-actions]

@launchdarkly/browser size report
This is the brotli compressed size of the ESM build.
Compressed size: 179649 bytes
Compressed size limit: 200000
Uncompressed size: 831617 bytes

[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.