Add py.typed to package_data of lark package

[hf-kklein]

Based on #1106 (comment)
Fixes #1105

(py39) python setup.py build
running build
running build_py
package init file 'lark\grammars\__init__.py' not found (or not a regular file)
copying lark\py.typed -> build\lib\lark

[hf-kklein]

obsoletes #1106
alternative to #1108

[erezsh]

Looks right.

Did you test it?

[hf-kklein]

Did you test it?

Not up to my own library ;) But in the build/lib/lark directory the file is now included. At least it won't do any harm.

[hf-kklein]

I could give it a try when using a pip dev-install of lark instead of the published 1.1.0 in the library where the problem occured in #1105.

[erezsh]

If you see the file in a fresh build, that's probably proof enough.

[hf-kklein]

I just verified it:

• checked out Hochfrequenz/ahbicht/lark-1.1.0
• ran mypy src/ahbicht (or tox -re type_check) => fail
• used pip install -q -e ../lark to install this lark branch
• used mypy src/ahbicht again => success

[erezsh]

Good enough for me.