fix: fix duplicated injected style tags when using shadow dom

We are currently checking that the style element exists in the shadow dom to decide if it already exists in the head

Author: Loïc Mangeonjean

vscode-patches/0064-feat-support-shadow-dom.patch

@@ -840,7 +840,7 @@ index 27d04d09f01..61c2b58dfa4 100644
  			active = active.parentElement;
  		}
 diff --git a/src/vs/workbench/services/themes/browser/workbenchThemeService.ts b/src/vs/workbench/services/themes/browser/workbenchThemeService.ts
-index d85b23015f4..d7d186e8234 100644
+index d85b23015f4..9dc47531aea 100644
 --- a/src/vs/workbench/services/themes/browser/workbenchThemeService.ts
 +++ b/src/vs/workbench/services/themes/browser/workbenchThemeService.ts
 @@ -18,7 +18,7 @@ import { Event, Emitter } from '../../../../base/common/event.js';
@@ -857,7 +857,7 @@ index d85b23015f4..d7d186e8234 100644
 
  function _applyRules(styleSheetContent: string, rulesClassName: string) {
 -	const themeStyles = mainWindow.document.head.getElementsByClassName(rulesClassName);
-+	const themeStyles = (shadowRootContainer ?? mainWindow.document.head).querySelectorAll(`.${rulesClassName}`);
++	const themeStyles = mainWindow.document.head.querySelectorAll(`.${rulesClassName}`);
  	if (themeStyles.length === 0) {
  		const elStyle = createStyleSheet();
  		elStyle.className = rulesClassName;