[Support] Move StringExtras.h include from Error.h to Error.cpp (part 5)

[IncludeGuardian]

Summary

1st commit
[lldb] Add missing StringExtras.h includes

In preparation for removing the #include "llvm/ADT/StringExtras.h"
from the header to source file of llvm/Support/Error.h, first add in
all the missing includes that were previously included transitively
through this header.

This is fixing all files missed in b0abd4893fa1, 39d8e6e22cd1,
a11efd49266f, and 5551657b310b.

---

2nd commit
[Support] Move StringExtras.h include from Error.h to Error.cpp

Move the implementation of the toString function from
llvm/Support/Error.h to the source file, which allows us to move
#include "llvm/ADT/StringExtras.h" to the source file as well.

As Error.h is present in a large number of translation units this
means we are unnecessarily bringing in the contents of
StringExtras.h - itself a large file with lots of includes - and
slowing down compilation.

Also move the #include "llvm/ADT/SmallVector.h" directive to the
source file as it's no longer needed, but this does not give as much of
a benefit.

This reduces the total number of preprocessing tokens across the LLVM
source files in lib from (roughly) 1,920,413,050 to 1,903,629,230 - a
reduction of ~0.87%. This should result in a small improvement in
compilation time.

[IncludeGuardian]

lldb/tools/lldb-vscode/VSCode.cpp

20

This should be the final failure on the last time landing the Error.h change to main https://lab.llvm.org/buildbot#builders/68/builds/55847

[MaskRay]

Still, would be good to land the lldb commit separately. And ensure that you have performed the last-minute testing...
Ensure that projects like flang bolt still build.

lldb/tools/lldb-vscode/VSCode.cpp

 //===-- VSCode.cpp ----------------------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include <chrono>
 #include <cstdarg>
 #include <fstream>
 #include <mutex>
 #include <sstream>
 
 #include "LLDBUtils.h"
 #include "VSCode.h"
+#include "llvm/ADT/StringExtras.h"
 #include "llvm/Support/FormatVariadic.h"
 
 #if defined(_WIN32)
 #define NOMINMAX
 #include <fcntl.h>
 #include <io.h>
 #include <windows.h>
 #endif
 
 using namespace lldb_vscode;