Add metadata to `FileSystem`

[james-pre]

Instead of using many different functions for checking metadata about a FileSystem, it would be cleaner and more organized to use a metadata property. For example:

export interface FileSystemMetadata {
    name: string;
    readonly: boolean;
    synchronous: boolean;
    supportsProperties: boolean;
    supportsLinks: boolean;
    totalSpace: number;
    freeSpace: number;
}

export abstract class FileSystem {
    abstract readonly metadata: FileSystemMetadata;
}

Implementations would use getters or readonly to ensure that users can not modify the file system's metadata.

[james-pre]

Added in 4f6ce99