Auto merge of #112070 - lcnr:disjoint-closure-capture-ub, r=oli-obk

change `BorrowKind::Unique` to be a mutating `PlaceContext`

fixes #112056

I believe that `BorrowKind::Unique` is a footgun in general, so I added a FIXME and opened https://github.com/rust-lang/rust/issues/112072. This is a bit too involved for this PR though.

compiler/rustc_mir_transform/src/const_prop.rs

@@ -772,7 +772,6 @@ impl<'tcx> Visitor<'tcx> for CanConstProp {
             // mutation.
             | NonMutatingUse(NonMutatingUseContext::SharedBorrow)
             | NonMutatingUse(NonMutatingUseContext::ShallowBorrow)
-            | NonMutatingUse(NonMutatingUseContext::UniqueBorrow)
             | NonMutatingUse(NonMutatingUseContext::AddressOf)
             | MutatingUse(MutatingUseContext::Borrow)
             | MutatingUse(MutatingUseContext::AddressOf) => {

compiler/rustc_mir_transform/src/copy_prop.rs

@@ -130,7 +130,6 @@ impl<'tcx> MutVisitor<'tcx> for Replacer<'_, 'tcx> {
             PlaceContext::NonMutatingUse(
                 NonMutatingUseContext::SharedBorrow
                 | NonMutatingUseContext::ShallowBorrow
-                | NonMutatingUseContext::UniqueBorrow
                 | NonMutatingUseContext::AddressOf,
             ) => true,
             // For debuginfo, merging locals is ok.

compiler/rustc_mir_transform/src/ssa.rs

@@ -216,7 +216,6 @@ impl<'tcx> Visitor<'tcx> for SsaVisitor<'_> {
             PlaceContext::NonMutatingUse(
                 NonMutatingUseContext::SharedBorrow
                 | NonMutatingUseContext::ShallowBorrow
-                | NonMutatingUseContext::UniqueBorrow
                 | NonMutatingUseContext::AddressOf,
             )
             | PlaceContext::MutatingUse(_) => {