Auto merge of #25344 - arielb1:fresh-float, r=nikomatsakis

There is no subtyping relationship between the types (or their non-freshened
variants), so they can not be merged.

Fixes #22645
Fixes #24352
Fixes #23825

Should fix #25235 (no test in issue).
Should fix #19976 (test is outdated).

diff --cc src/librustc/middle/traits/select.rs
Simple merge

diff --cc src/librustc/middle/ty.rs
Simple merge