align isPowerlineGlyph across renderers (#3743)

src/browser/renderer/RendererUtils.ts

@@ -9,3 +9,9 @@ export function throwIfFalsy<T>(value: T | undefined | null): T {
   }
   return value;
 }
+
+export function isPowerlineGlyph(codepoint: number): boolean {
+  // This range was established via
+  // https://apw-bash-settings.readthedocs.io/en/latest/fontpatching.html
+  return 0xE000 <= codepoint && codepoint <=  0xF8FF;
+}