Export math-static-elements.ts for using static element types

[tsuji-riya]

MathSpanElement (and related static element types) were not accessible from the public types, making it impossible to pass type check mathSpanElement.render() even if using TypeScript.

I added export * from './math-static-elements' to src/public/mathlive.ts.
This exposes MathSpanElement, MathDivElement so I can type-check references to / elements and call their methods without casting to any or unknown.

Example

import type { MathSpanElement } from 'mathlive';
const mathSpanRef = useRef<MathSpanElement>(null);

mathSpanRef.current?.render();

return (<math-span ref={mathSpanRef} />);