clang-format: Add IncludeBlocks: Preserve

The same change and reasoning as
c077eefc1e5007a5c656183737e82d5c0a7df855 in build/soong, copied below:

As of [1], the Google format, which we default to, uses IncludeBlocks:
Regroup, which sorts all includes with <> and without .h into the top
group reserved for libc headers, e.g.:

+#include <android-base/properties.h>
+#include <android-base/strings.h>
 #include <ctype.h>
 #include <stdlib.h>
 #include <sys/system_properties.h>

 #include <iostream>

-#include <android-base/properties.h>
-#include <android-base/strings.h>

This is accurate to the Google C++ style guide, which states that
other library headers should be included with "", however we have a
strong tendency to use <> for these headers for Android, so we must
revert this change.

Note, clang-format allows regexes for creating the blocks as well,
however, short of including all possible libc headers, I don't think
there's a way to differentiate between <sys/wait.h> and
<other_lib/header.h>.

[1]:
62e3198c4f (diff-b689ebff2e51e675b346a88289e74542)

Test: clang-format doesn't do the above.
Change-Id: I2e3f6ee75fd725b620174082afcce4ee7f4efa66

.clang-format

@@ -12,3 +12,4 @@ UseTab: Never
 PenaltyExcessCharacter: 32
 
 Cpp11BracedListStyle: false
+IncludeBlocks: Preserve