Rollup merge of #148080 - GuillaumeGomez:fix-jump-def-links, r=lolbinarycat

[rustdoc] Fix invalid jump to def macro link generation

Follow-up of rust-lang/rust#147820.

I realized that when there was no intra-doc link linking to the same item, then the generated link for macros in jump to def would be invalid.

To make the code less redundant, I merged the "registering" of items and the href generation use the same code for macros.

r? `````@notriddle`````

Author: Zalathar