Fix optional parameter metadata emission

[DavidObando]

Summary

• centralize source parameter-row emission so methods, explicit/primary constructors, interfaces, delegates, and managed interop surfaces emit CLR Optional/HasDefault flags plus Constant rows
• normalize constants to the declared parameter type and reject mismatched or unsupported CLR metadata constants without changing G# omitted-argument materialization
• add metadata, reflection, ILVerify, G# runtime, and real Roslyn C# consumer regressions across numeric, string, enum, bool, char, floating-point, and nil defaults

Validation

• targeted optional emit tests: 16 passed
• targeted optional binding tests: 16 passed
• full Core.Tests: 6,691 passed, 1 skipped
• full Compiler.Tests: 3,384 passed; 19 environment-only failures because Gsharp.Extensions.dll had not been built; after building it, all affected classes passed (128/128)
• RC-C13-6 Oahu rerun: rebuilt Oahu.Cli.App and Oahu.Cli.Tui with this compiler, then compiled the full C# test corpus against them; CS7036 fell from 12 reported failures to 0

Deferred

• Oahu still reports unrelated ABI/nullability families (CS1729, CS1739, CS8858, CS8602/CS8604, CS8613, CS8766); these map to the separately reported RC-C13-5/7 and nullable-fidelity work.

Fixes #2745