[PM-14351] Migrate away from theme enum (#11812)

* update extension autofill concerns to use theme object and type over enum

* mark ThemeType enum as deprecated

* update theming service concerns to use theme object and type over enum

libs/common/src/platform/enums/theme-type.enum.ts

@@ -1,3 +1,6 @@
+/**
+ * @deprecated prefer the `ThemeTypes` constants and `Theme` type over unsafe enum types
+ **/
 export enum ThemeType {
   System = "system",
   Light = "light",
@@ -5,3 +8,13 @@ export enum ThemeType {
   Nord = "nord",
   SolarizedDark = "solarizedDark",
 }
+
+export const ThemeTypes = {
+  System: "system",
+  Light: "light",
+  Dark: "dark",
+  Nord: "nord",
+  SolarizedDark: "solarizedDark",
+} as const;
+
+export type Theme = (typeof ThemeTypes)[keyof typeof ThemeTypes];