Move source editor out of module (#12457)

* Update Copybara options in preparation for open-sourcing the source editor

* Move files

* Update paths

* Remove source-editor module and checks for its existence

* Explicitly mention CM6 license in files that contain code adapted from CM6

GitOrigin-RevId: 89b7cc2b409db01ad103198ccbd1b126ab56349b

services/web/webpack-plugins/lezer-grammar-compiler.js

@@ -1,9 +1,6 @@
 const fs = require('fs')
 const path = require('path')
-const modulePath = path.resolve(
-  __dirname,
-  '../modules/source-editor/scripts/lezer-latex/generate.js'
-)
+const modulePath = path.resolve(__dirname, '../scripts/lezer-latex/generate.js')
 
 try {
   fs.accessSync(modulePath, fs.constants.W_OK)