PDL: Add a python parser implementation for environments without rust

This implementation is a partial implementation that don't emit
`comments`, `loc` or `file`
It also assumes that the pdl file is valid

Test: atest --host pypdl_test
(cherry picked from https://android-review.googlesource.com/q/commit:b16b82282652692c20cfcdaa3de82b023ee73cf3)
Merged-In: Ic15748d83920b30b25b3dac3e07919ea117c2fc0

Cherry picked with conflicts

Change-Id: Iae63c1c0db174b2ffe2cc25339295035cbcddeb6