Migrate to TypeScript 6/7 #19226

Replace typescript with @typescript/native-preview (tsgo) for type checking and declaration generation. tsgo is Microsoft's Go-based rewrite of the TypeScript compiler, promising up to 10x faster builds and significantly reduced memory usage.

⚠️ tsgo is still in preview and not production ready.

This is exploratory work to validate feasibility, surface required code changes, and track upstream progress toward a stable release. Upgrading to TypeScript 6.0 first may be a good bridge step, it's the last JS-based release and deprecates the features removed in 7.0, letting us fix compatibility issues incrementally before the full native switch.

Known blockers

• Some packages still need fixes to build cleanly under tsgo
• Declaration emit is not fully complete upstream (some types get dropped during exports)
• --build mode (project references) still has gaps
• Aligns with TS 5.9 semantics, some deprecated patterns may need migration

Depends on

• TypeScript 6.0 release (bridge step)
• TypeScript 7.0 reaching RC / stable
• Upstream completion of declaration emit and --build support
• Dropping TS 3.8 type generation

Tracking PR: https://github.com/getsentry/sentry-javascript/pull/18422