feat(lang): add F# support

[CalvinAllen]

Description

Add support for F# projects and source files.

Current Behavior

The extension currently only handles:

• .cs files for namespace and using statement updates
• .csproj files for project file updates

Proposed Changes

• Update SourceFileService to handle .fs files
• Update namespace patterns for F# syntax (namespace OldName / module OldName)
• Update open patterns (open OldName)
• Handle .fsproj files in ProjectFileService

F# Syntax Examples

// Namespace declaration
namespace OldName

// Module declaration
module OldName.Something

// Open statement
open OldName
open OldName.SubNamespace

Priority

Low - enhancement for broader language support