Add Inline temp variable code action

[william-laverty]

Description

Add a syntactic code action that inlines a temporary variable by replacing all references to it with its initializer expression, then removing the declaration.

Changes

• New InlineTempVariable code action in Sources/SwiftLanguageService/CodeActions/
• Registered in allSyntaxCodeActions
• Tests for basic inlining, parenthesization of binary expressions, and non-offering for unused variables

Behavior

The action is offered when the cursor is on a let/var declaration that:

• Has a single binding with an initializer
• Has no type annotation
• Is referenced in subsequent statements
• Is not used as an inout argument or reassigned

Smart parenthesization wraps the inlined expression when it's a binary operation, ternary, try/await, or cast expression to preserve precedence.

Before:

let basePrice = item.price
let total = basePrice * quantity

After:

let total = item.price * quantity

Resolves #2507

[ahoppen]

@william-laverty I appreciate your enthusiasm but you now have 7 open PRs. I would encourage you to leave it at that for now so that you have the time and energy to address review feedback on those.

[ahoppen]

Here, again, we already have a PR that implements this. #2529