Avoid lookbehind (not supported in Safari)

build/azure-pipelines/darwin/product-build-darwin.yml

@@ -159,7 +159,7 @@ steps:
       set -e
       yarn test-browser --build --browser chromium --browser webkit --browser firefox --tfs "Browser Unit Tests"
     displayName: Run unit tests (Browser)
-    timeoutInMinutes: 10
+    timeoutInMinutes: 5
     condition: and(succeeded(), eq(variables['VSCODE_ARCH'], 'x64'), eq(variables['VSCODE_STEP_ON_IT'], 'false'))
 
   - script: |

src/vs/editor/contrib/linesOperations/linesOperations.ts

@@ -1056,7 +1056,11 @@ export class SnakeCaseAction extends AbstractCaseAction {
 	}
 
 	protected _modifyText(text: string, wordSeparators: string): string {
-		return text.replace(/(?<=\p{Ll})(\p{Lu})|(?<!\b|_)(\p{Lu})(?=\p{Ll})/gmu, '_$&').toLocaleLowerCase();
+		return (text
+			.replace(/(\p{Ll})(\p{Lu})/gmu, '$1_$2')
+			.replace(/([^\b_])(\p{Lu})(\p{Ll})/gmu, '$1_$2$3')
+			.toLocaleLowerCase()
+		);
 	}
 }