Removed duplicated checks reported by cppcheck

In C++17, static constexpr members are implicitly inline, so they no
longer require an out-of-line definition.

Identified with readability-redundant-declaration.

This reverts 4d10c1165442cbbbc0017b48fcdd7dae1ccf3678 and its two
dependent commits: e6b9805b574bb5c90263ec7fbcb94df76d2807a4 and
c243406a695ca056a07ef4064b0f9feee7685320, see discussion in
https://github.com/llvm/llvm-project/pull/165598#issuecomment-3563825509.

d076608d58d1ec55016eb747a995511e3a3f72aa moved some deps around to avoid
cycles and left clang/Frontend/FrontendDiagnostic.h as a shim that
simply includes clang/Basic/DiagnosticFrontend.h. This PR inlines it so
that nothing in tree still includes clang/Frontend/FrontendDiagnostic.h.

Doing this will help prevent future layering issues. See #162865.

Frontend already depends on Basic, so no new deps need to be added
anywhere except for places that do strict dep checking.

This patch fixes and eliminates the possibility of SupportFileSP ever
being nullptr. The support file was originally treated like a value
type, but became a polymorphic type and therefore has to be stored and
passed around as a pointer.

To avoid having all the callers check the validity of the pointer, I
introduced the invariant that SupportFileSP is never null and always
default constructed. However, without enforcement at the type level,
that's fragile and indeed, we already identified two crashes where
someone accidentally broke that invariant.

This PR introduces a NonNullSharedPtr to prevent that. NonNullSharedPtr
is a smart pointer wrapper around std::shared_ptr that guarantees the
pointer is never null. If default-constructed, it creates a
default-constructed instance of the contained type. Note that I'm using
private inheritance because you shouldn't inherit from standard library
classes due to the lack of virtual destructor. So while the new
abstraction looks like a `std::shared_ptr`, it is in fact **not** a
shared pointer. Given that our destructor is trivial, we could use
public inheritance, but currently there's no need for it.

rdar://164989579

NFC patch which moves `DiagnosticsRendering` from `Utility` to `Host`.

This refactoring is needed for
https://github.com/llvm/llvm-project/pull/168603. It adds a method to
check whether the current terminal supports Unicode or not. This will be
OS dependent and a better fit for `Host`. Since `Utility` cannot depend
on `Host`, `DiagnosticsRendering` must live in `Host` instead.

A function prologue can begin with a pre-index STR instruction for a
floating-point register. To construct an unwind plan from assembly
correctly, the instruction emulator must support such instructions.

This patch adds `LLDBLog::InstrumentationRuntime` as a log channel to
provide an appropriate channel for instrumentation runtime plugins as
previously one did not exist.

A small use of the channel is added to illustrate its use. The logging
added is not intended to be comprehensive.

This is primarily motivated by an `-fbounds-safety` instrumentation
plugin (https://github.com/swiftlang/llvm-project/pull/11835).

rdar://164920875

In this PR we are proposing to change LLDB codebase so that LLDB is able
to print values of integer registers that have more than 64-bits (even
if the number of bits is not equal to 128).

---------

Co-authored-by: Matej Košík <matej.kosik@codasip.com>
Co-authored-by: Jonas Devlieghere <jonas@devlieghere.com>