[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 b0abd48, 39d8e6e,
a11efd4, 5551657, and 90bfe2d.

Differential Revision: https://reviews.llvm.org/D155178

Author: elliotgoodrich

lldb/unittests/Symbol/PostfixExpressionTest.cpp

@@ -9,6 +9,7 @@
 #include "lldb/Symbol/PostfixExpression.h"
 #include "lldb/Utility/DataExtractor.h"
 #include "lldb/Utility/StreamString.h"
+#include "llvm/ADT/StringExtras.h"
 #include "llvm/DebugInfo/DIContext.h"
 #include "llvm/DebugInfo/DWARF/DWARFExpression.h"
 #include "llvm/Support/FormatVariadic.h"

lldb/unittests/SymbolFile/NativePDB/UdtRecordCompleterTests.cpp

@@ -7,6 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "Plugins/SymbolFile/NativePDB/UdtRecordCompleter.h"
+#include "llvm/ADT/StringExtras.h"
 #include "gmock/gmock.h"
 #include "gtest/gtest.h"