Add Rust Environment module

[makubacki]

Adds helpers for checking if a firmare environment is ready to build Rust.

The primary purpose of the functionality in rust_environment is to be used in a build plugin wrapper. However, the public functions may be used in other contexts as well.

[codecov]

Codecov Report

Attention: Patch coverage is 86.56716% with 18 lines in your changes missing coverage. Please review.

Project coverage is 78.70%. Comparing base (bf643b0) to head (0f4f29c).
Report is 82 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #848      +/-   ##
==========================================
- Coverage   78.75%   78.70%   -0.05%     
==========================================
  Files          49       41       -8     
  Lines        4909     5049     +140     
==========================================
+ Hits         3866     3974     +108     
- Misses       1043     1075      +32     

Files	Coverage Δ
edk2toolext/environment/rust.py	86.56% <86.56%> (ø)

... and 49 files with indirect coverage changes

[Javagedes]

Thanks for writing tests.