lldbUtility seems like a more suitable place for StreamBuffer.

Differential Revision: https://reviews.llvm.org/D157463

This is a follow-up to https://reviews.llvm.org/D140896, split into
several parts as it touches a lot of files.

Differential Revision: https://reviews.llvm.org/D141298

This patch replaces (llvm::|)Optional< with std::optional<.  I'll post
a separate patch to clean up the "using" declarations, #include
"llvm/ADT/Optional.h", etc.

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

This patch adds #include <optional> to those files containing
llvm::Optional<...> or Optional<...>.

I'll post a separate patch to actually replace llvm::Optional with
std::optional.

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

This patch mechanically replaces None with std::nullopt where the
compiler would warn if None were deprecated.  The intent is to reduce
the amount of manual work required in migrating from Optional to
std::optional.

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

Fix #57799

Before, NativePDB uses scoped range as a workaround for value range, that causes
problems (e.g. a variable's value can only have one range, but usually a
variable's value is located at different address ranges, each at different
locations, in optimized build).
This patch let NativePDB switch to DWARFLocationList so a variable's value can
be described at multiple non-overlapped address ranges and each range maps to a
location.
Because overlapping ranges exists, here's peference when choosing ranges:
1. Always prefer whole value locations. Suppose a variable size is 8 bytes, one record is that for range [1, 5) first 4 bytes is at ecx, and another record is that for range [2, 8) the 8 bytes value is at rdx. This results: [1, 2) has first 4 bytes at ecx, [2, 8) has the whole value at rdx.
2. Always prefer the locations parsed later. Suppose first record is that for range [1, 5) value is at ecx, second record is that for range [2, 6) value is at eax. This results: [1, 2) -> ecx, [2, 6) -> eax.

Differential Revision: https://reviews.llvm.org/D130796

This reland 227dffd0b6d78154516ace45f6ed28259c7baa48 and
562c3467a6738aa89203f72fc1d1343e5baadf3c with failed api tests fixed by keeping
function base file addres in DWARFExpressionList.

This reverts commit 227dffd0b6d78154516ace45f6ed28259c7baa48 and its
follow up 562c3467a6738aa89203f72fc1d1343e5baadf3c because it breaks a
bunch of tests on GreenDragon:

https://green.lab.llvm.org/green/view/LLDB/job/lldb-cmake/45155/

Differential Revision: https://reviews.llvm.org/D125509