Clean task doesn't have access to build configuration/code

[Xymanek]

The clean task is currently a separate script, which is already problematic:

• Fix mod project paths containing spaces #56 isn't applied to cleaning logic
• clean_cooker_output.ps1 had to be a separate file (it's called from both clean and build) and duplicates logic from build:
  

  X2ModBuildCommon/clean_cooker_output.ps1

  Lines 6 to 8 in 9c81722

  	# TODO: duplicates the logic in build_common.ps1
  	$actualTfcSuffix = "_$($modNameCanonical)_DLCTFC_XPACK_"
  	$cookerOutputPath = [io.path]::combine($sdkPath, 'XComGame', 'Published', 'CookedPCConsole')

• clean.ps1 is forced to use some flaky logic due to lack of access to project's ContentOptions.json
  

  X2ModBuildCommon/clean.ps1

  Lines 22 to 24 in 9c81722

  	# This needs to be before $srcDirectory\BuildCache is deleted - otherwise we will miss our collection maps
  	# This is dumb, yes, but to fix this we need to rework how BuildProject is used from build.ps1 (and here)
  	CleanModAssetCookerOutput $sdkPath $modName @("$srcDirectory\$modName\ContentForCook", "$srcDirectory\BuildCache\CollectionMaps")

Fixing this however requires significantly changing how individual projects consume X2MBC (and some internal refactor of X2MBC)

cc @robojumper