[compiler] Add fault tolerance plan document

[josephsavona]

Add detailed plan for making the React Compiler fault-tolerant by
accumulating errors across all passes instead of stopping at the first
error. This enables reporting multiple compilation errors at once.

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Stack created with Sapling. Best reviewed with ReviewStack.

• [compiler] Fix Pipeline.ts early-exit, formatting, and style issues #35853
• [compiler] Rename mismatched variable names after type changes #35852
• [compiler] Remove local CompilerError accumulators, emit directly to env.recordError() #35851
• [compiler] Remove tryRecord, add catch-all error handling, fix remaining throws #35850
• [compiler] Cleanup: consistent tryRecord() wrapping and error recording #35849
• [compiler] Add fault tolerance test fixtures #35848
• [compiler] Phase 3: Make lower() always produce HIRFunction #35847
• [compiler] Phase 8: Add multi-error test fixture and update plan #35845
• [compiler] Phase 4 (batch 2), 5, 6: Update remaining passes for fault tolerance #35844
• [compiler] Phase 4 (batch 1): Update validation passes to record errors on env #35843
• [compiler] Phase 2+7: Wrap pipeline passes in tryRecord for fault tolerance #35842
• [compiler] Phase 1: Add error accumulation infrastructure to Environment #35841
• -> [compiler] Add fault tolerance plan document #35840