Add a 'throwIfNamespace' option for JSX transform (#6563)

* Added tests for ifThrowNamespace flag

* JSX transformator could work with XMLNamespaces (ifThrowNamespace flag)

* Use template literal instead

* Attempt to reword the message

* Added docs

* Reworded docs

* Reworded docs

* Fixed missing space in error message

packages/babel-plugin-transform-react-jsx/src/index.js

@@ -3,6 +3,8 @@ import helper from "@babel/helper-builder-react-jsx";
 
 export default function({ types: t }, options) {
   const pragma = options.pragma || "React.createElement";
+  const throwIfNamespace =
+    options.throwIfNamespace === undefined ? true : !!options.throwIfNamespace;
 
   const JSX_ANNOTATION_REGEX = /\*?\s*@jsx\s+([^\s]+)/;
 
@@ -20,6 +22,8 @@ export default function({ types: t }, options) {
     post(state, pass) {
       state.callee = pass.get("jsxIdentifier")();
     },
+
+    throwIfNamespace,
   });
 
   visitor.Program = function(path, state) {