fix(codegen): print static keyword for TSIndexSignature

[Dunqing]

The codegen was missing the static keyword when printing TSIndexSignature
nodes, causing static [key: string]: string index signatures to lose the
static modifier during code generation.

Co-Authored-By: Claude Opus 4.6 noreply@anthropic.com

[Dunqing]

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This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
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• fix(codegen): print static keyword for TSIndexSignature #19755 👈 (View in Graphite)
• fix(codegen): print override keyword for method and property definitions #19753
• main

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[codspeed-hq]

Merging this PR will not alter performance

✅ 52 untouched benchmarks
⏩ 3 skipped benchmarks¹

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_{Comparing fix/codegen-static-index-signature (8cad8f5) with main (ed17bbf)}

Footnotes

1. 3 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩