Rewrite SCSS compilation in Bash

[kdmccormick]

Background

Part of:

• Build edx-platform assets without Paver #31604

Subtasks

• Create a sh (not bash) script scripts/assets/compile-sass.sh, re-implementing the functionality of pavelib/assets.py:_compile_sass.
• Replace the implemention of pavelib/assets.py:_compile_sass with a simple call to the new shell script.

Notes

This is blocked by upgrading to node-sass or dart-sass. That's because, with libsass-python (our current compliation mechanism), there are two ways to compile Sass, and neither are satisfactory:

• The Python API (sass.compile(..)), which we currently use, cannot not be elegantly called from a shell script. It'd have to be implemented with brittle command along the lines of:

  python -c "import sass; sass.compile(dirname=('$sass_src', '$css_dest'), include_paths=$include_paths, ... )"

  where $include_paths would have to be stitched together, in shell. That all sounds like a step backwards rather than in improvement.
• The command line interface that comes with the library, sassc does not accept directories as parameters, only individual files. We'd need to implement the logic to compile every file in a directory ourselves.

[kdmccormick]

would be Resolved by #31583

[kdmccormick]

Closed in favor of the parent issue: #31604