Improve resolveConfig return type: merge themes (#12272)

* Generate types: do not intersect with Config theme type when generating DefaultTheme

* Merge default theme in ResolvedConfig

* UnwrapResolvables on theme.extend as well

* Apply extend to overrides and default theme

* Omit extend from DefaultTheme

* Relax generic constraints, better generic variable names

* Fall back to ThemeConfig if key not in DefaultTheme

* Split out ThemeConfigCustomizable to avoid anys in ThemeConfigResolved

* Allow custom theme properties

* handle TypeScript error

* apply prettier formatting

* update changelog

* change type name

---------

Co-authored-by: Nikita Gaidakov <ngaidakov@podfather.com>
Co-authored-by: Robin Malfait <malfait.robin@gmail.com>

scripts/generate-types.js

@@ -91,9 +91,8 @@ fs.writeFileSync(
   path.join(process.cwd(), 'types', 'generated', 'default-theme.d.ts'),
   prettier.format(
     `
-    import { Config } from '../../types'
     type CSSDeclarationList = Record<string, string>
-    export type DefaultTheme = Config['theme'] & { ${defaultThemeTypes} }
+    export type DefaultTheme = { ${defaultThemeTypes} }
   `,
     {
       semi: false,