Feature/more quick fixes

[chrisdp]

Add new quick fixes and fix-all code actions

Expands the code actions processor with several new quick fixes and "fix all" variants:

• Missing imports: "Fix all: Auto fixable missing imports" aggregates all unambiguous missing import fixes across the file in a single action
• Void return values: fix or fix-all for removing return values from subs/void functions
• Return type declarations: fix or fix-all for removing return types from sub declarations, and adding void return types to function declarations
• Convert function to sub: quick fix for functions that should be subs (single only, no fix-all)
• Script import cleanup: fix or fix-all for removing redundant parent script imports, unnecessary codebehind imports, and correcting import path casing (now preserving relative paths)

Also introduces a shared emitOrFixAll() helper that standardizes the pattern of emitting a single fix vs. a "fix all" composite action.