Consolidate native diagnostic formatting and diagnostic parsing helpers

[doublemover]

Parent inventory: #8108

Objective

Consolidate duplicated native diagnostic construction, normalization-adjacent helpers, and diagnostic coordinate parsing.

Shared Module Specification

• Extend native/objc3c/src/diag/objc3_diag_utils.* or add a dependency-neutral diagnostic helper module if that avoids cycles.
• Expose one MakeDiag-equivalent formatter preserving exact line:column: message [CODE] semantics.
• Expose diagnostic code/coordinate parsing helpers used by grammar/source precision checks.
• Keep parser/sema/lex dependency direction clean.
• Prefer simple unsigned scanning for diagnostic coordinate parsing over exception-heavy numeric parsing.

Migration Checklist

• Migrate duplicate MakeDiag implementations where dependency direction allows.
• Migrate duplicated diagnostic coordinate parsing helpers.
• Migrate FlattenStageDiagnostics only if the shared diagnostic utility is the correct owner.
• Preserve exact diagnostic text and sorting behavior.
• Update CMake target dependencies if a source file moves across libraries.

Complete Replacement Inventory

• MakeDiag - 6 definition(s)/local occurrence(s) to replace or explicitly document as intentionally local if semantics differ.
  • native/objc3c/src/lex/objc3_lexer.cpp:54
  • native/objc3c/src/parse/objc3_parse_support.cpp:109
  • native/objc3c/src/pipeline/objc3_frontend_artifacts.cpp:11077
  • native/objc3c/src/sema/objc3_pure_contract.cpp:10
  • native/objc3c/src/sema/objc3_sema_pass_manager.cpp:36
  • native/objc3c/src/sema/objc3_semantic_passes.cpp:16
• FlattenStageDiagnostics - 2 definition(s)/local occurrence(s) to replace or explicitly document as intentionally local if semantics differ.
  • native/objc3c/src/io/objc3_diagnostics_artifacts.cpp:56
  • native/objc3c/src/pipeline/objc3_frontend_artifacts.cpp:11083
• StartsWith - 2 definition(s)/local occurrence(s) to replace or explicitly document as intentionally local if semantics differ.
  • native/objc3c/src/parse/objc3_diagnostic_grammar_hooks_core_feature.cpp:9
  • native/objc3c/src/parse/objc3_diagnostic_source_precision_scaffold.cpp:8
• TryParseUnsignedSegment - 2 definition(s)/local occurrence(s) to replace or explicitly document as intentionally local if semantics differ.
  • native/objc3c/src/parse/objc3_diagnostic_grammar_hooks_core_feature.cpp:14
  • native/objc3c/src/parse/objc3_diagnostic_source_precision_scaffold.cpp:13
• TryParseDiagnosticCoordinateAndCode - 2 definition(s)/local occurrence(s) to replace or explicitly document as intentionally local if semantics differ.
  • native/objc3c/src/parse/objc3_diagnostic_grammar_hooks_core_feature.cpp:34
  • native/objc3c/src/parse/objc3_diagnostic_source_precision_scaffold.cpp:34

Performance And Reliability Requirements

• Keep helper code small, dependency-light, and fast enough for normal development feedback.
• Add focused tests for edge cases before broad migration.
• Preserve existing output schemas and public behavior unless an intentional bug fix is validated.
• Keep production helpers separated from test-only helpers.
• Do not use tmp/ as durable source-of-truth; generated temporary files are allowed only as transient command inputs.

Fast Tests

• Run diagnostic utility tests.
• Run lexer/parser/sema diagnostic tests affected by MakeDiag changes.
• Run native build.
• Run focused frontend diagnostics checks.
• Run git diff --check.

End-To-End Completion Criteria

• Diagnostic formatting has one authoritative implementation where dependency direction permits.
• Diagnostic coordinate parsing has one authoritative implementation.
• Diagnostic output remains byte-for-byte compatible except for intentional validated bug fixes.

[doublemover]

Completed in 5166b5588.

Validation:

• python -m py_compile scripts/check_objc3c_diag_utils.py scripts/check_objc3c_native_json_helper.py
• python scripts/check_objc3c_diag_utils.py
• clang++ -std=c++20 -I native/objc3c/src -fsyntax-only native/objc3c/src/diag/objc3_diag_utils.cpp native/objc3c/src/parse/objc3_parse_support.cpp
• python scripts/check_objc3c_dependency_boundaries.py --strict
• python scripts/check_objc3c_native_json_helper.py
• pwsh -NoProfile -File scripts/build_objc3c_native.ps1 -ExecutionMode binaries-only
• python scripts/build_objc3c_editor_tooling_surface.py
• python scripts/objc3c_public_workflow_runner.py check-public-command-contract
• python scripts/check_objc3c_runtime_acceptance.py --suite fast
• git diff --check

Note: pwsh -NoProfile -File scripts/run_objc3c_diagnostics_regression_suite.ps1 still reports 243/250 passing with existing unexpected-code fixture failures: O3P100/O3S260 in draft/container diagnostics fixtures.