Clang-Format: Sort include directives by letter, not by ASCII code

[mmoderau]

When sorting includes in a project, that mixes case styles for file names (for example both PascalCase and snake_case), it would be helpful to be able to sort alphabetically (case aware) instead of by character code.

Currently

#include <AClass.h>
#include <ThisIsADifferentClass.h>
#include <a_header_with_utility_functions.h>

Expected

#include <AClass.h>
#include <a_header_with_utility_functions.h>
#include <ThisIsADifferentClass.h>

[mkurdej]

The option SortIncludes gained CaseInsensitive some time ago (in v13). You might give it a try.
Cf. a8105b3