Auto merge of rust-lang#132325 - lcnr:damn-son, r=<try>

rework winnowing to sensibly handle global where-bounds

this is somewhat weird, but it at least allows us to mirror this behavior in the new solver:
- trivial builtin-impls
- non-global where-bounds, bailing with ambiguity if at least one global where-bound exists
- object ☠️ + alias-bound candidates
- merge candidates ignoring global where-bounds

This is a different approach from rust-lang#124592 which maintains the "if there are global where-bounds, don't guide type inference using non-global where-bounds" behavior, hopefully avoiding the breakage and means we use guidance from non-global where-bounds in fewer, instead of in more cases.

r? `@compiler-errors`

Author: bors

compiler/rustc_trait_selection/src/lib.rs

@@ -23,6 +23,7 @@
 #![feature(extract_if)]
 #![feature(if_let_guard)]
 #![feature(iter_intersperse)]
+#![feature(iterator_try_reduce)]
 #![feature(let_chains)]
 #![feature(never_type)]
 #![feature(rustdoc_internals)]