The legacy llvm::identity is not quite the same as std::identity from
C++20.  llvm::identity is a template struct with an ::argument_type
member.  In contrast, llvm::identity_cxx20 (and std::identity) is a
non-template struct with a templated call operator and no
::argument_type.

This patch modernizes llvm::SparseSet by updating its default
key-extraction functor to llvm::identity_cxx20.  A new template
parameter KeyT takes over the role of ::argument_type.

Existing uses of SparseSet are updated for the new template signature.
Most use sites are of the form SparseSet<T>, requiring no update.

We can not trust that !HasFallThrough implies that there is not
fallthrough exit in cases when analyzeBranch failed.

Adding a new blockNeverFallThrough helper to make the tests on
!HasFallThrough safe by also checking IsBrAnalyzable. We also
try to prove no-fallthrough by inspecting the successor list. If
the textual successor isn't in the successor list we know that
there is no fallthrough.

The bug has probably been around for years. Found it when
working on an out-of-tree target.

Add per-property has<Prop>/set<Prop>/reset<Prop> functions to
MachineFunctionProperties.

We can use *Set::insert_range to collapse:

  for (auto Elem : Range)
    Set.insert(E);

down to:

  Set.insert_range(Range);

Fixes the "use after poison" issue introduced by #121516 (see
<https://github.com/llvm/llvm-project/pull/121516#issuecomment-2585912395>).

The root cause of this issue is that #121516 introduced "Called Global"
information for call instructions modeling how "Call Site" info is
stored in the machine function, HOWEVER it didn't copy the
copy/move/erase operations for call site information.

The fix is to rename and update the existing copy/move/erase functions
so they also take care of Called Global info.

Identified with misc-include-cleaner.

This `AA` parameter is not used and for most uses they just pass
a nullptr.

The use of `AA` was removed since 8d0383e.

- Add `MachineBlockFrequencyAnalysis`.
- Add `MachineBlockFrequencyPrinterPass`.
- Use `MachineBlockFrequencyInfoWrapperPass` in legacy pass manager.
- `LazyMachineBlockFrequencyInfo::print` is empty, drop it due to new
pass manager migration.

This reverts commit ab58b6d58edf6a7c8881044fc716ca435d7a0156.
In `CodeGen/Generic/MachineBranchProb.ll`, `llc` crashed with dumped MIR
when targeting PowerPC. Move test to `llc/new-pm`, which is X86
specific.