Add Remove unused parameter code action

[william-laverty]

Description

Add a syntactic code action that removes a function parameter not referenced in the function body and updates call sites within the same file.

Changes

• New RemoveUnusedParameter code action in Sources/SwiftLanguageService/CodeActions/
• Registered in allSyntaxCodeActions
• Tests for removal with call site updates and non-offering for used parameters

Behavior

The action is offered when the cursor is on a parameter in a function declaration where:

• The parameter's local name is not _
• The function has a body
• The parameter name is not referenced anywhere in the function body

Call site updates:

• Finds function calls by matching the function name and argument label at the expected position
• Handles removal of first, middle, and last arguments correctly (including comma cleanup)
• Only updates call sites in the same file (syntactic limitation)

Before:

func greet(name: String, title: String) {
    print("Hello, \\(name)")
}

greet(name: "Alice", title: "Ms.")

After:

func greet(name: String) {
    print("Hello, \\(name)")
}

greet(name: "Alice")

Resolves #2513

[ahoppen]

Same here, there’s already a PR that addresses this: #2530