Add xercesc parsing of environment variables in the xml path

[dudarboh]

BEGINRELEASENOTES

• Add xercesc parsing of environment variables in the xml path xml parsing problem? iLCSoft/Marlin#60

ENDRELEASENOTES

See iLCSoft/Marlin#60 for the discussion.

This hard fixes it for me. But there is probably a cleaner way of doing it...
I am not an expert, so please cross-check.

[github-actions]

Test Results

   11 files     11 suites   5h 40m 41s ⏱️
  366 tests   165 ✅ 0 💤 201 ❌
1 506 runs  1 301 ✅ 0 💤 205 ❌

For more details on these failures, see this check.

Results for commit 5fe1774.

♻️ This comment has been updated with latest results.

[dudarboh]

I moved the function to the top of the file... Seems to work...

[andresailer]

I just want to have @MarkusFrankATcernch comment on this, in case there is some side-effect from resolving environment variables here that could clash with other variables we resolve.

[MarkusFrankATcernch]

Hmm..... This environment resolution mechanism is always a bit tricky and very often one runs into contradicting requirements.
Formally this all looks OK to me.
If all tests work I think this is fine. If people start to complain we can have a look at real use cases.

[MarkusFrankATcernch]

The environment resolution mechanism is always a bit tricky and very often one runs into contradicting requirements.
Formally this all looks OK to me.
If all tests work I think this is fine. If people start to complain we can have a look at real use cases.