build: import XModule source SCSS directly rather than copying

The `xmodule_assets` command copies SCSS source files from
xmodule/css to common/static/xmodule/scss, renaming them
to `{MD5_HASH}.scss` in order to "remove duplicates".
The copied files are then included into the generated
SCSS entrypoint files (eg AnnotatableBlockStudio.scss).

The "de-deplication" is completely unnecessary: there are
only a couple dozen SCSS files, and none of them are duplicates.
This copying process is confusing, it complicates our
build process, and it makes our SCSS harder to understand.

So, in the generated SCSS entrypoint files, we
stop importing the *copied* SCSS sources, and just
import the *original* SCSS sources instead.
For example, common/static/xmodule/descriptors/scss/AboutBlockStudio.scss
is changed from:

    .xmodule_edit.xmodule_AboutBlock {
      @import "9bdcda00f046f78be79aca7791e1d4fb.scss";
      @import "a10fc3e0fd6aca63426a89e75fe69c31.scss";
    }

to:

    .xmodule_edit.xmodule_AboutBlock {
      @import "editor/edit.scss";
      @import "html/edit.scss";
    }

In order to make the `@import` lines work, we add xmodule/css to the list
of lookup dirs for XModule SCSS compilation. We also remove the
copying logic from `xmodule_assets`, as it is no longer needed.

Part of: openedx#32292

pavelib/assets.py

@@ -172,6 +172,7 @@ def get_theme_sass_dirs(system, theme_dir):
     certs_css_dir = theme_dir / system / "static" / "certificates" / "css"
     xmodule_sass_folder = "modules" if system == 'lms' else "descriptors"
     xmodule_sass_dir = path("common") / "static" / "xmodule" / xmodule_sass_folder / "scss"
+    xmodule_lookup_dir = path("xmodule") / "css"
 
     dependencies = SASS_LOOKUP_DEPENDENCIES.get(system, [])
     if sass_dir.isdir():
@@ -202,7 +203,9 @@ def get_theme_sass_dirs(system, theme_dir):
         dirs.append({
             "sass_source_dir": xmodule_sass_dir,
             "css_destination_dir": path("common") / "static" / "css" / "xmodule",
-            "lookup_paths": dependencies + [
+            "lookup_paths": [
+                xmodule_lookup_dir,
+                *dependencies,
                 sass_dir / "partials",
                 system_sass_dir / "partials",
                 system_sass_dir,
@@ -237,6 +240,7 @@ def get_system_sass_dirs(system):
     css_dir = path(system) / "static" / "css"
     xmodule_sass_folder = "modules" if system == 'lms' else "descriptors"
     xmodule_sass_dir = path("common") / "static" / "xmodule" / xmodule_sass_folder / "scss"
+    xmodule_lookup_dir = path("xmodule") / "css"
 
     dependencies = SASS_LOOKUP_DEPENDENCIES.get(system, [])
     dirs.append({
@@ -251,7 +255,9 @@ def get_system_sass_dirs(system):
     dirs.append({
         "sass_source_dir": xmodule_sass_dir,
         "css_destination_dir": path("common") / "static" / "css" / "xmodule",
-        "lookup_paths": dependencies + [
+        "lookup_paths": [
+            xmodule_lookup_dir,
+            *dependencies,
             sass_dir / "partials",
             sass_dir,
         ],

xmodule/static_content.py

@@ -126,29 +126,20 @@ def _write_styles(selector, output_root, classes, css_attribute, suffix):
     into `output_root` as individual files
     """
     contents = {}
+    xmodule_scss_path = resource_filename(__name__, "") + "/css/"
 
     for class_ in classes:
         class_css = getattr(class_, css_attribute)()
-        fragment_paths = class_css.get('scss', [])
-        if not fragment_paths:
-            continue
-        fragment_names = []
-        for fragment_path in fragment_paths:
-            with open(fragment_path, 'rb') as fragment_file:
-                fragment = fragment_file.read()
-            fragment_name = "{hash}.{type}".format(
-                hash=hashlib.md5(fragment).hexdigest(),
-                type='scss')
-            # Prepend _ so that sass just includes the files into a single file
-            filename = '_' + fragment_name
-            contents[filename] = fragment
-            fragment_names.append(fragment_name)
+        rel_fragment_paths = []
+        for fragment_path in class_css.get('scss', []):
+            rel_fragment_path = fragment_path.split(xmodule_scss_path)[1]
+            rel_fragment_paths.append(rel_fragment_path)
 
         module_styles_lines = []
         module_styles_lines.append("""{selector}.xmodule_{class_.__name__} {{""".format(
             class_=class_, selector=selector
         ))
-        module_styles_lines.extend(f'  @import "{name}";' for name in fragment_names)
+        module_styles_lines.extend(f'  @import "{path}";' for path in rel_fragment_paths)
         module_styles_lines.append('}')
 
         contents[f"{class_.__name__}{suffix}.scss"] = '\n'.join(module_styles_lines)