fix(dts): try the .json file itself after .d.json.ts for json imports

[ocavue]

resolve_dts only tried .d.json.ts for import "./data.json" and never the .json file itself, so JSON imports failed under the dts resolver even though TypeScript's bundler mode resolves them (resolveJsonModule defaults to true there).

This mirrors tryAddingExtensions in TypeScript (linked in the code comments): https://github.com/microsoft/TypeScript/blob/v6.0.3/src/compiler/moduleNameResolver.ts#L2155-L2158

Re-implements #1052, which was merged into a stacked branch and never reached main.

[codspeed]

Merging this PR will degrade performance by 6.78%

❌ 5 regressed benchmarks
✅ 16 untouched benchmarks
⏩ 5 skipped benchmarks¹

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Benchmark	BASE	HEAD	Efficiency
❌	pm/npm-flat	1.8 ms	2 ms	-10.05%
❌	resolver_real[multi-thread]	496.2 µs	543.5 µs	-8.7%
❌	pm/bun-flat	1.8 ms	1.9 ms	-5.23%
❌	pm/bun-isolated	2 ms	2.1 ms	-5.09%
❌	pm/yarn-flat	1.8 ms	1.9 ms	-4.72%

Tip

Investigate this regression by commenting @codspeedbot fix this regression on this PR, or directly use the CodSpeed MCP with your agent.

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_{Comparing ocavue:fix/dts-json-extension (7c07330) with main (0ac26d9)}

Footnotes

1. 5 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. ↩