Decouple XModule styles from LMS/Studio styles (attempt 2) (#32188)

This basically changes how the xmodule static files are
generated and consumed in order to separate the Xblock
styles from general style files. Includes:

* build: decople XModule style assets by using a custom webpack loader
* build: move scss imports to its specific file
* build: fix: add system dirs to theme lookup paths. 

This is an amendment to #32018

Addressing the issue #31624

xmodule/css/html/display.scss

@@ -1,4 +1,7 @@
+@import 'vendor/bi-app/bi-app-ltr';
 @import 'bourbon/bourbon';
+@import 'lms/theme/variables';
+@import 'lms/theme/variables-v1';
 
 // HTML component display:
 * {