[FIX] bundle/Builder: Remove sourceMappingURL from modules embedded a…

…s string

Leaving the reference will cause browser development tools to create
unnecessary requests. The minify task will always add these references,
and we already remove them in all other bundling modes.

In the case I analyzed (internal ref 2380057784), the source map
requests even used incorrect URLs containing the string '<unknown>',
possibly because they are only created when the module es eval'ed.

lib/lbt/bundle/Builder.js

@@ -439,7 +439,20 @@ class BundleBuilder {
 		} else if ( /\.js$/.test(moduleName) /* implicitly: && info != null && info.requiresTopLevelScope */ ) {
 			log.warn(
 				`Module ${moduleName} requires top level scope and can only be embedded as a string (requires 'eval')`);
-			outW.write( makeStringLiteral( (await resource.buffer()).toString() ) );
+			let moduleContent = (await resource.buffer()).toString();
+			if (this.options.sourceMap) {
+				// We are actually not interested in the source map this module might contain,
+				// but we should make sure to remove any "sourceMappingURL" from the module content before
+				// writing it to the bundle. Otherwise browser dev-tools might create unnecessary (and likely incorrect)
+				// requests for any referenced .map files
+				({moduleContent} =
+					await this.getSourceMapForModule({
+						moduleName,
+						moduleContent,
+						resourcePath: resource.getPath()
+					}));
+			}
+			outW.write( makeStringLiteral(moduleContent) );
 		} else if ( /\.html$/.test(moduleName) ) {
 			const fileContent = (await resource.buffer()).toString();
 			outW.write( makeStringLiteral( fileContent ) );