Use mount instead of preload for tagfiles

[anutosh491]

Description

Please include a summary of changes, motivation and context for this PR.

Fixes #305
Closes #295

As discussed on the issue

1. xcpp.data should only be responsible for standard headers or resource dir headers
2. As tagfiles for any 3rd party lib would be expected to be picked up from the prefix, we should do the same for the tagfiles we provide.

Type of change

Please tick all options which are relevant.

• Bug fix
• New feature
• Added/removed dependencies
• Required documentation updates

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.78%. Comparing base (3a888b6) to head (c802afe).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #336   +/-   ##
=======================================
  Coverage   81.78%   81.78%           
=======================================
  Files          20       20           
  Lines         950      950           
  Branches       87       87           
=======================================
  Hits          777      777           
  Misses        173      173           

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[anutosh491]

Should probably go in only after the pr using the shared build for xeus.

[anutosh491]

cc @SylvainCorlay , this should be ready.

[mcbarton]

You are still preloading these paths in the test executable too

https://github.com/anutosh491/xeus-cpp/blob/c802afe18f04343157fa036e436e809cd0529aad/test/CMakeLists.txt#L79

so needs removing there too.

[anutosh491]

so needs removing there too.

No, for the tests we are not building using jupyter lite build so we can't use empack's mount feature there.

The only way we can make it available in the file system is through emscripten's preload, so that remains as it is.

If you go through the issue, you will understand that its only xcpp.data that this issue and the pr is concerned about and not any other .data file (which is test_xeus_cpp.data in this case)

It seems that Matthew's point has been addressed by Anutosh's comment.

[anutosh491]

This works as expected