[BOLT] Use std::nullopt instead of None (NFC)

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 ma

[BOLT] Use std::nullopt instead of None (NFC)

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

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[BOLT][NFC] Fix file-description comments

Summary: Fix comments at the start of source files.

(cherry picked from FBD33274597)

[BOLT][NFC] Reformat with clang-format

Summary: Selectively apply clang-format to BOLT code base.

(cherry picked from FBD33119052)

[BOLT][NFC] Do not pass BinaryContext alongside BinaryFunction

Summary:
BinaryContext is available via BinaryFunction::getBinaryContext(),
hence there's no reason to pass both as arguments to a func

[BOLT][NFC] Do not pass BinaryContext alongside BinaryFunction

Summary:
BinaryContext is available via BinaryFunction::getBinaryContext(),
hence there's no reason to pass both as arguments to a function.

In a similar fashion, BinaryBasicBlock has an access to BinaryFunction
via getFunction(). Eliminate unneeded arguments.

(cherry picked from FBD31921680)

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Rebase: [NFC] Refactor sources to be buildable in shared mode

Summary:
Moves source files into separate components, and make explicit
component dependency on each other, so LLVM build system knows h

Rebase: [NFC] Refactor sources to be buildable in shared mode

Summary:
Moves source files into separate components, and make explicit
component dependency on each other, so LLVM build system knows how to
build BOLT in BUILD_SHARED_LIBS=ON.

Please use the -c merge.renamelimit=230 git option when rebasing your
work on top of this change.

To achieve this, we create a new library to hold core IR files (most
classes beginning with Binary in their names), a new library to hold
Utils, some command line options shared across both RewriteInstance
and core IR files, a new library called Rewrite to hold most classes
concerned with running top-level functions coordinating the binary
rewriting process, and a new library called Profile to hold classes
dealing with profile reading and writing.

To remove the dependency from BinaryContext into X86-specific classes,
we do some refactoring on the BinaryContext constructor to receive a
reference to the specific backend directly from RewriteInstance. Then,
the dependency on X86 or AArch64-specific classes is transfered to the
Rewrite library. We can't have the Core library depend on targets
because targets depend on Core (which would create a cycle).

Files implementing the entry point of a tool are transferred to the
tools/ folder. All header files are transferred to the include/
folder. The src/ folder was renamed to lib/.

(cherry picked from FBD32746834)

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