Grafana UI: Use package.json exports for internal code (#101815)

* feat(grafana-ui): introduce development exports to prevent importing from grafana/ui/src

* refactor(theme-generation): move theme templates into scripts so themes continue to build

* refactor(frontend): replace  grafana/ui paths that use nested src with /internal or /unstable

* chore(betterer): update better results file

* feat(grafana-ui): support enterprise, remove Text component from internal

* docs(packages): update readme with exporting code conventions

scripts/cli/themeTemplates/generatedFileBanner.ts

@@ -0,0 +1,10 @@
+export const renderGeneratedFileBanner = (themeFile: string, templateFile: string) => `/***
+ * !!! THIS FILE WAS GENERATED AUTOMATICALLY !!!
+ *
+ * Do not modify this file!
+ * - Edit ${themeFile} to regenerate
+ * - Edit ${templateFile} to update template
+ *
+ * !!! THIS FILE WAS GENERATED AUTOMATICALLY !!!
+ */
+`;