Pex

This release brings another fix for pathologically slow cases of lock
creation as well as a new `--sh-boot` feature for creating PEXes that
boot via `/bin/sh` for more resilience across systems with differing
Python installations as well as offering lower boot latency.

* Support booting via `/bin/sh` with `--sh-boot`. (1721)
* Fix more pathologic lock creation slowness. (1723)

This release fixes `--lock` resolving for certain cases where extras are
involved as well as introducing support for generating and consuming
portable `--find-links` locks using `-path-mapping`.

* Fix `--lock` resolver extras handling. (1719)
* Support canonicalizing absolute paths in locks. (1716)

This release fixes missing artifacts in non-`strict` locks.

* Don't clear lock link database during analysis. (1712)

This release fixes pathologically slow cases of lock creation as well as
introducing support for `--no-compression` to allow picking the
time-space tradeoff you want for your PEX zips.

* Fix pathologic lock creation slowness. (1707)
* Support uncompressed PEXes. (1705)

This release finalizes spurious deadlock handling in `--lock` resolves
worked around in 1694 in Pex 2.1.75.

* Fix lock_resolver to use BSD file locks. (1702)

This release fixes a deadlock when building PEXes in parallel via the
new `--lock` flag.

* Avoid deadlock error when run in parallel. (1694)