Auto merge of #137940 - 1c3t3a:alignment-borrows-check, r=saethlin

Extend the alignment check to borrows

The current alignment check does not include checks for creating misaligned references from raw pointers, which is now added in this patch.

When inserting the check we need to be careful with references to field projections (e.g. `&(*ptr).a`), in which case the resulting reference must be aligned according to the field type and not the type of the pointer.

r? `@saethlin`

cc `@RalfJung,` after our discussion in #134424

Author: bors