Improve transform-react-jsx typings

[JLHwung]

Q	A
Tests Added + Pass?	Yes
Documentation PR Link
Any Dependency Changes?
License	MIT

This PR starts by improving typings of transform-react-jsx, the type checker catches unreachable statements in

babel/packages/babel-plugin-transform-react-jsx/src/create-plugin.ts

Lines 95 to 103 in 58a65e9

	for (const attr of path.get("attributes")) {
	if (!attr.isJSXElement()) continue;
	const { name } = attr.node.name;
	if (name === "__source" || name === "__self") {
	throw path.buildCodeFrameError(
	`__source and __self should not be defined in props and are reserved for internal usage.`,
	);
	}

The guard should have been !attr.isJSXAttribute(). However, since we have already thrown selfSourceError in automatic runtime

babel/packages/babel-plugin-transform-react-jsx/src/create-plugin.ts

Line 692 in 58a65e9

if (found[name]) throw sourceSelfError(path, name);

and we allow multiple __self and __source in classical runtime. I think current behavior is ok so we can simply remove the unreachable statements.

This PR also exports a PluginPass type from @babel/core, which can be used by plugin authors.

[babel-bot]

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