Repeated links in the same page should have the same alias/code

Vimium creates new character combinations for each link it finds, even if it's the same link.

It's fine for text inputs or # but otherwise it just bloats the page with more (and more complex) combinations when it could reuse the same when another link in the same page with the same URL was already assigned one.

I made a quick test to show it is indeed the case:

A probably more complex but awesome feature (once this is implement) would be to hide repeated hints when they are very close. Many sites (like Github, YouTube, Google) have many elements with the same links bunched up, makes it hard to read and to know which one is which when they are actually all (or many) the same

The issue does not name files or tests; start by locating Vimium's hint-generation entry point and tracing how links receive character combinations. Reproduce the case with repeated URLs, preserving separate hints for text inputs or # links, and verify that repeated non-# links reuse an assigned alias.