Parser does not respect the `escape` directive

[camdencheek]

The Dockerfile reference includes an escape directive which lets you set the escape character for the file. This appears to be fairly widely used, particularly for Windows Dockerfiles. However, it is not yet respected by this parser. It will likely storing some state in an external parser as described here.

[ahlinc]

I've left an additional comment for you here: https://github.com/tree-sitter/tree-sitter/discussions/1100#discussioncomment-726482 related to this issue, please, give it a look.