Adds more garbage collection settings

[TheAngryByrd]

WHAT

🤖 Generated by Copilot at d3992b2

This pull request adds new settings to control FSAC's garbage collection and deprecates conserveMemory. It updates package.json and LanguageService.fs to reflect these changes.

🤖 Generated by Copilot at d3992b2

If you use FSAC for F# coding
You might want to tweak its eroding
Of memory and heap
With settings more deep
Than conserveMemory, now exploding

🗑️🚀🗃️

WHY

• Deprecated FSharp.fsac.conserveMemory and added FSharp.fsac.gc.conserveMemory. I think it's reasonable to allow people to configure this with whatever value they want. Defaulted it to off.
• Added FSharp.fsac.gc.heapCount with a default value of 2. This should allow us to still get some benefits of server GC while not having a heap per core which could look like we're using more memory than we should.
• Added FSharp.fsac.gc.server with default value of on. We do ship FSAC with this on but this allows people to turn it off if they really want to have a bit more control over their memory.

HOW

🤖 Generated by Copilot at d3992b2

• Add and update settings for FSAC garbage collector configuration (link, link, link, link)
• Deprecate FSharp.fsac.conserveMemory setting in package.json and show a message to use FSharp.fsac.gc.conserveMemory instead (link)
• Add FSharp.fsac.gc.conserveMemory, FSharp.fsac.gc.heapCount, and FSharp.fsac.gc.server settings in package.json with default values, descriptions, and validation rules (link)
• Replace conserveMemory option with gcConserveMemory, gcHeapCount, and gcServer options in getOptions function in LanguageService module in src/Core/LanguageService.fs and assign them the values from the settings (link)
• Pass DOTNET_GCHeapCount, DOTNET_GCConserveMemory, and DOTNET_GCServer environment variables to FSAC process in spawnNetCore function in LanguageService module in src/Core/LanguageService.fs and format DOTNET_GCHeapCount as hexadecimal (link)
• Bump up extension version to 7.8.1 in package.json (link)