Fix Sass source maps with absolute paths in sources

[thatmattlove]

Proposed Changes

Figure out how to use a relative path, or disable sourcemaps for Sass files altogether.

See:

• sourcemap support for CSS evanw/esbuild#519
• Source maps + publicPath evanw/esbuild#1290
• Relative Url Rewriting glromeo/esbuild-sass-plugin#19

Justification

As-is, the absolute path of the source file is included in Sass maps, for example:

{
  "version": 3,
  "sources": ["sass:/Users/ml/dev/netbox/netbox/project-static/styles/_cable_trace.scss"],
  "mappings": "...",
  "names": []
}

JavaScript sourcemaps, on the other hand, contain relative paths. For example:

{
  "version": 3,
  "sources": ["../src/select/api/apiSelect.ts"],
  "mappings": "...",
  "names": []
}