Initial check in - Support other JSX factories Issue #3788

- added jsxNamespace compile option
- when jsx mode is "react", jsxNamespace optionally specifies the emit namespace for React calls, eg "--jsxNamespace MyDOMLib" will emit calls as MyDOMLib.createElement (instead of React.createElement)
- symbol specified by jsxNamespace must be present, else compile error is generated (same handling as is done for React symbol when no jsxNamespace is specified)

src/compiler/commandLineParser.ts

@@ -54,6 +54,11 @@ namespace ts {
             description: Diagnostics.Specify_JSX_code_generation_Colon_preserve_or_react,
             error: Diagnostics.Argument_for_jsx_must_be_preserve_or_react
         },
+        {
+            name: "jsxNamespace",
+            type: "string",
+            description: Diagnostics.Specify_JSX_emit_namespace_when_JSX_code_generation_mode_is_react
+        },
         {
             name: "listFiles",
             type: "boolean",