Migrate all the non react components code to typescript (#847)

This completes the migration to typescript of all the non react
components code.
The only changes introduced besides types are the type checks using
`"something" in object` which narrows down types in typescript.

src/libs/field-spec-additional.ts

@@ -0,0 +1,18 @@
+const spec = {
+  maputnik: {
+    maptiler_access_token: {
+      label: "MapTiler Access Token",
+      doc: "Public access token for MapTiler Cloud."
+    },
+    thunderforest_access_token: {
+      label: "Thunderforest Access Token",
+      doc: "Public access token for Thunderforest services."
+    },
+    style_renderer: {
+      label: "Style Renderer",
+      doc: "Choose the default Maputnik renderer for this style.",
+    },
+  }
+}
+
+export default spec;