Preserve explicit class constructor ABI in cs2gs

[DavidObando]

Summary

• stop all explicit class constructor lifting at the shared AnalyzeConstructorLift root
• preserve original constructor parameter names, private field visibility, and property getters through the normal constructor/member translators
• cover Oahu OutputContext/CapabilityPolicy and a field-backed class through translation, gsc compilation, and a real C# named-argument/property/reflection consumer
• keep native C# primary constructors covered as the negative case

Scope and issue mapping

• Included here (cs2gs: primary-constructor reshaping breaks constructor and property ABI #2746 / PR Preserve explicit class constructor ABI in cs2gs #2760): every explicit class constructor that previously flowed through class-to-primary reshaping, including property-backed and field-only T2 forms
• Records: structurally separate synthesized data class/data struct metadata path; tracked by gsc: data class and data struct metadata is not C# record compatible #2744 (open, no implementation PR yet)
• Plain/value-type explicit constructors: structurally separate because G# structs reject in-body init and cs2gs uses primary-constructor/call-site literal lowering; reproduced with a real C# consumer and filed as cs2gs/gsc: explicit struct constructor lowering breaks C# consumer ABI #2766. Earlier cs2gs: struct with multiple ctors that can't lift to primary-ctor form emits invalid init(...) on struct #1990/cs2gs: struct with multiple instance constructors can be silently omitted #2435 only fixed invalid/dropped translation and same-language call sites

No ABI case discovered in this audit is left untracked.

Validation

• targeted generalized ABI/regression tests: 9 passed
• MSBUILDDISABLENODEREUSE=1 dotnet test tools/cs2gs/Cs2Gs.Tests/Cs2Gs.Tests.csproj -c Release --no-build --no-restore --nologo: 1,728 passed on latest main

Fixes #2746