Identified with misc-include-cleaner.

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

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

This change implements the contextual symbolizer markup elements: reset,
module, and mmap. These provide information about the runtime context of
the binary necessary to resolve addresses to symbolic values.

Summary information is printed to the output about this context.
Multiple mmap elements for the same module line are coalesced together.
The standard requires that such elements occur on their own lines to
allow for this; accordingly, anything after a contextual element on a
line is silently discarded.

Implementing this cleanly requires that the filter drive the parser;
this allows skipped sections to avoid being parsed. This also makes the
filter quite a bit easier to use, at the cost of some unused
flexibility.

Reviewed By: peter.smith

Differential Revision: https://reviews.llvm.org/D129519

This allows registering certain tags as possibly beginning multi-line
elements in the symbolizer markup parser. The parser is kept agnostic to
how lines are delimited; it reports the entire contents, including line
endings, once the end of element marker is reached.

Reviewed By: peter.smith

Differential Revision: https://reviews.llvm.org/D124798

This adds a parser for the log symbolizer markup format discussed in
https://discourse.llvm.org/t/rfc-log-symbolizer/61282. The parser
operates in a line-by-line fashion with minimal memory requirements.

This doesn't yet include support for multi-line tags or specific parsing
for ANSI X3.64 SGR control sequences, but it can be extended to do so.
The latter can also be relatively easily handled by examining the
resulting text elements.

Reviewed By: peter.smith

Differential Revision: https://reviews.llvm.org/D124686