[meta] Consolidate filesystem path operations. #8541

Tasks:

• find all direct usage of node's "path" module
  • see: grep -l "'path'" src/client/**/*.ts | xargs grep -ho 'path\.[a-zA-Z]*' | sort | uniq
  • dirname()
  • extend()
  • extname()
  • isAbsolute()
  • join()
  • length()
  • relative()
  • resolve()
  • toLocaleLowerCase()
  • toString()
  • toUpperCase()
• how to deal with third-party modules that use node's "path" module directly?
• prep (especially for testability)
  • add IFileSystemPaths for low-level API (see [meta] Code health for filesystem interaction. #8801)
  • move IPathUtils around & rename it (see [meta] Code health for filesystem interaction. #8801)
  • move low-level operations to IFileSystemPaths (meta: [meta] Code health for filesystem interaction. #8801)
  • move high-level operations to IFileSystemPathUtils (meta: [meta] Code health for filesystem interaction. #8801)
• consolidate all fs path operations
  • target: IFileSystemPaths
    • join()
      • (Update the code base to use IFileSystem instead of fs and fs-extra. #7915) implement
      • update call sites to use IFileSystemPathUtils.raw.*
    • dirname()
      • (Update the code base to use IFileSystem instead of fs and fs-extra. #7915) implement
      • update call sites to use IFileSystemPathUtils.raw.*
    • basename()
      • update call sites to use IFileSystemPathUtils.raw.*
    • (Update the code base to use IFileSystem instead of fs and fs-extra. #7915) normcase()
      • implement
      • update call sites to use IFileSystemPathUtils.raw.*
    • sep
      • update call sites to use IFileSystemPathUtils.raw.*
    • ...
  • target: IFileSystemPaths
    • ...
• ensure we keep using only our wrapper in the future (see [meta] Code health for filesystem interaction. #8801)