feat!: Move JSX from global namespace to vhtml.JSX

Instead of injecting the `JSX` namespace as a global symbol, move it
under a new namespace named `vhtml`.
This `vhtml` namespace is merged with the `vhtml()` function. Library
consumers can access it as `.JSX`:

    import h from "vhtml";
    type A = h.JSX.Element;

The `JSX` namespace can also be imported directly:

    import h, {JSX} from "vhtml";
    type A = JSX.Element;

This should allow vhtml-powered JSX code to be used together with other
JSX-based libraries, such as React. It _should_ solve the issue:

- developit/vhtml#19 (comment)

Background: TypeScript 2.8 supports locally scoping the `JSX` namespace.
This allows a package to use multiple libraries that expose different
variations of the `JSX` namespace without conflicts.

See:
- https://www.typescriptlang.org/docs/handbook/release-notes/typescript-2-8.html#locally-scoped-jsx-namespaces
- microsoft/TypeScript#22207

Note: This does not allow you to use two JSX-based libraries together
in a single module. No transpiler that I know of supports this use case.

Author: pastelmind

input/vhtml.d.ts

@@ -46,8 +46,8 @@ declare function vhtml<Props, Children extends any[]>(
  */
 type HtmlElementAttr<
   Tag extends string
-> = (Tag extends keyof JSX.IntrinsicElements
-  ? JSX.IntrinsicElements[Tag]
+> = (Tag extends keyof vhtml.JSX.IntrinsicElements
+  ? vhtml.JSX.IntrinsicElements[Tag]
   : {}) & {
   dangerouslySetInnerHTML?: { __html: string };
   [attr: string]: any;
@@ -99,7 +99,7 @@ type ComponentPropTransform<TComp, TProps> = SafeEmptyType<
     ? never
     : {});
 
-declare global {
+declare namespace vhtml {
   namespace JSX {
     type Element = string;
 

src/generate-types.ts

@@ -210,9 +210,9 @@ function generateJsxTypesForVhtml(
 
   // Since extracting interfaces from reactSourceFile takes very long, let's do
   // this first so that we can fail fast if the input source file doesn't have
-  // `global.JSX`.
+  // `vhtml.JSX`.
   const inputJsxNamespace = inputSourceFile
-    .getModuleOrThrow("global")
+    .getModuleOrThrow("vhtml")
     .getModuleOrThrow("JSX");
 
   const extractedInterfaceNodes: (