Fix type exports and enable isolatedModules setting to catch it in tsc (#2197)

This is the same issue as the one I fixed last year in #1874

To prevent this from occurring again, I enabled the `isolatedModules`
Typescript option which will warn when you export non-value identifiers
without using `export type`, which will break transpilation processes
what work on a per-file basis. You can find a [more detailed explanation
in Typescript's
doc](https://www.typescriptlang.org/tsconfig#isolatedModules)

src/ReactNativeSVG.ts

@@ -141,15 +141,6 @@ export {
   camelCase,
   err,
   fetchText,
-  JsxAST,
-  Middleware,
-  Styles,
-  UriProps,
-  UriState,
-  XmlAST,
-  XmlProps,
-  XmlState,
-  AstProps,
   Shape,
   RNSVGMarker,
   RNSVGMask,
@@ -175,4 +166,16 @@ export {
   RNSVGForeignObject,
 };
 
+export type {
+  JsxAST,
+  Middleware,
+  Styles,
+  UriProps,
+  UriState,
+  XmlAST,
+  XmlProps,
+  XmlState,
+  AstProps,
+};
+
 export default Svg;