[v3] LiteAdaptor's elementsByClass() fails to return any elements.

The LiteAdaptor's elementsByClass() throws an error about the class.find() argument. In particular

https://github.com/mathjax/MathJax-src/blob/28233c6d2d3ffea10cd223c11903e4e97079a8ce/ts/adaptors/liteAdaptor.ts#L197-L198

should use classes.includes(name) rather than classes.find(name), and tags.push(n) rather than tags = [].