FileSystemProvide API should declare enums starting with 1

[dbaeumer]

The type in question is:

	export enum FileType {
		File = 0,
		Dir = 1,
		Symlink = 2
	}

Having 0 as a value only causes problems with default interpretation and the absence of properties. I only use 0 if this is equal to the property no being there.

[jrieken]

Yeah, makes sense

[siegebell]

It also needed documentation :) -- I wasn't sure whether it was describing bit flags or discrete options until vscode gave me errors for describing a file as a Symlink but not allowing readdir.

[jrieken]

Started on this... @siegebell Do you have a preference? I have some changes in joh/fs-next that allow for a bit mask but maybe discrete options are better. (I have a preference for the latter)

export enum FileType {
  File = 1,
  Dir = 2,
  Symlink = 64
}
export interface FileStat {
  mtime: number;
  size: number;
  type: FileType;
}

or

export enum FileType {
  File = 1,
  Dir = 2,
}
export interface FileStat {
  mtime: number;
  size: number;
  type: FileType;
  isSymlink: boolean;
}