FB Release v2020.06.29.01 + BigSur compatibility patch

This includes:

• all commits from FaceBuck through the 2020.06.29.01 release
• all commits from Addepar's fork played on top of the 2020.06.29.91 release
• a special cherry-pick of facebook@a2912b9 with merge conflict resolution, to support Big Sur.
• a specific delete of python interpreter change to retrofit to python 2.7

SHA1: b92f7140341007ff40f79ad65118f1b4e05e23f6

[2nd attempt] FB Master @ 0acbcbbed7274ba654b64d97414b28183649e51a

SHA: 809c8a0e29cf8eeb043347e8ffc87a2a4e4b285a

bin/buck build --config java.target_level=11 --config java.source_level=11  buck --show-output

FB Release v2019.10.17.01

SHA-1: a089ce35b06d0ae26c19bd58fa83ba8ffb8c2f67