GNU3 Demangler: fix substitution tracking, expressions, and type names

Substitution table and scoping:
- Fix generic lambda auto parameters: save/replace m_templateSubstitute
  with 'auto' placeholders for lambda-local T_/T0_/T1_ resolution
- Fix local-name template scoping with m_inLocalName flag
- Fix substitution table off-by-one for all-type template args
- Fix pointer-to-member type (case 'M'): set substitute=true per ABI
- Fix multi-character seq-id parsing (S10_, S11_, etc.)
- Fix DemangleUnresolvedType decltype (DT/Dt) prefix consumption
- Add forward template ref support for cv conversion operators
- Fix sr qualifier-list PushType and conditional E handling
- Fix multi-level sr scope resolution without N prefix
- Fix sr + unscoped template substitution table tracking
- Fix I...E argument pack handling (GCC I...E vs J...E)
- Fix Dp pack expansion to show '...' for concrete types

Expression formatting:
- Fix L_Z embedded mangled name template scope isolation
- Handle LZ<encoding>E function address template args
- cl expression: callable(args) format with function substitute tracking
- dt/pt expressions: obj.member and obj->member directly
- fp_/fp<N>_ placeholders in decltype return types
- Fix fL function-param scope validation
- Fix DemangleBaseUnresolvedName 'on' prefix consumption

Type names (Itanium ABI spec compliance):
- x/y: "long long"/"unsigned long long"
- a: "signed char" (distinct from 'c' = "char")
- n/o: "__int128"/"unsigned __int128"
- g: "__float128" via FloatType altName
- Dd/Df/De: "decimal64"/"decimal32"/"decimal128"
- Dh: "_Float16"
- Dp: always show "..." for pack expansion
- Fix 'n' literal: __int128 not __uint128
- Fix dot extension spacing

Cleanup:
- Remove unused NextIsOneOf, ReadUntil, DemangleInitializer
- Guard GetRaw/GetTemplateType/PrintTables behind GNUDEMANGLE_DEBUG
- Remove unreachable GetNameType C/D cases
- Remove dead BinaryExpression "." check

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>