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

It is almost always simpler to use {} instead of std::nullopt to
initialize an empty ArrayRef. This patch changes all occurrences I could
find in LLVM itself. In future the ArrayRef(std::nullopt_t) constructor
could be deprecated or removed.

This patch adds a new code transformation to the `MachineSink` pass,
that tries to sink copies of an instruction, when the copies can be folded
into the addressing modes of load/store instructions, or
replace another instruction (currently, copies into a hard register).

The criteria for performing the transformation is that:
* the register pressure at the sink destination block must not
  exceed the register pressure limits
* the latency and throughput of the load/store or the copy must not deteriorate
* the original instruction must be deleted

Reviewed By: dmgreen

Differential Revision: https://reviews.llvm.org/D152828

Differential Revision: https://reviews.llvm.org/D151424

This is part of an effort to migrate from llvm::Optional to
std::optional:

https://discourse.llvm.org/t/deprecating-llvm-optional-x-hasvalue-getvalue-getvalueor/63716

These files no longer use llvm::Optional.

I've converted all known uses of None to std::nullopt, so we no longer
need to include None.h.

This is part of an effort to migrate from llvm::Optional to
std::optional:

https://discourse.llvm.org/t/deprecating-llvm-optional-x-hasvalue-getvalue-getvalueor/63716