clang-format: do not sort include calls #14713

The SortIncludes flag in clang-format will not correctly identify main header file includes in sources (probably due to usage of brackets and full paths).

This results in broken code, if clang-format is applied to e.g.

https://github.com/bitcoin/bitcoin/blob/47ed24cf8aa7be3b778731b1f140ad9941157933/src/qt/test/wallettests.cpp#L1-L2

which will reorder the two includes alphabetically (u < w), and the util.h include will then fail to compile due to missing QString definition.

The IncludeIsMainRegex (std::string) (https://clang.llvm.org/docs/ClangFormatStyleOptions.html) option seems to be a better solution to the issue here, so closing this PR.