Ignore Modules v4 environment variables in `from_sourcing_file` (#10753)

* from_sourcing_file: fixed a bug + added a few ignored variables

closes #7536

Credits for this change goes to mgsternberg (original author of #7536)

The new variables being ignored are specific to Modules v4.

* Use Spack Executable in 'EnvironmentModifications.from_sourcing_file'

Using this class avoids duplicating lower level logic to decode
stdout and handle non-zero return codes

* Extracted a function that returns the environment after sourcing files

The logic in `EnvironmentModifications.from_sourcing_file` has been
simplified by extracting a function that returns a dictionary with the
environment one would have after sourcing the files passed as argument.

* Further refactoring of EnvironmentModifications.from_sourcing_file

Extracted a function that sanitizes a dictionary removing keys that are
blacklisted, but keeping those that are whitelisted. Blacklisting and
whitelisting can be done on literals or regex.

Extracted a new factory that creates an instance of
EnvironmentModifications from a diff of two environments.

* Added unit tests

* PS1 is blacklisted + more readable names for some variables

0 files changed, 0 insertions, 0 deletions