4497: Create LowerCtx on the fly r=matklad a=edwin0cheng

Previously we create `LowerCtx` at the beginning of lowering, however, the hygiene content is in fact changing between macro expression expanding. 

This PR change it to create the `LowerCtx` on the fly to fix above bug.

However, #4465 is not fixed by this PR, the goto-def is still not work yet. It only fixed the infer part. 

Co-authored-by: Edwin Cheng <edwin0cheng@gmail.com>