Consolidate F# optional parameters documentation

[Copilot]

The F# documentation for optional parameters was incomplete and fragmented across multiple files. The methods.md file only covered C# interop-style optional arguments using [<Optional; DefaultParameterValue>] attributes, while missing the native F# optional parameter syntax using ?.

This PR consolidates all optional parameter documentation into the parameters-and-arguments.md file with clear distinctions between the two forms:

1. Optional Arguments with Late Defaults (F# Native): Using ? syntax for F#-idiomatic optional parameters that are interpreted as F# option types
2. Optional Arguments with Early Defaults (C# Interop): Using [<Optional; DefaultParameterValue>] attributes for C# compatibility, introduced in F# 4.1

The methods.md file now simply references the comprehensive documentation in parameters-and-arguments.md, eliminating duplication and providing developers with a single authoritative source for all optional parameter information.

This addresses the concern raised in the issue that the F# language's native optional parameter mechanism was not covered in the documentation, which was "very curious" given how commonly this technique is used.

Fixes #45813.

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Internal previews

📄 File	🔗 Preview link
docs/fsharp/language-reference/members/methods.md	Methods
docs/fsharp/language-reference/parameters-and-arguments.md	Parameters and Arguments

[T-Gro]

Is this terminology used or explained anywhere else in the docs?

I understand from the implementation perspective what it means, but maybe puting the names late / early exposes too much detail here? (without further explanation).

[T-Gro]

Should also mention usage of defaultArg and shadowing to convert an optional argument to a value.
Possibly also mention the advantage - unlike "C# style extensions", this allows authors of the method to tell if caller passed in a value or not.