Add include categories to .clang-format

This adds 3 rules that clang-format uses when ordering include files:
 - common.h is assigned priority -1
 - Incudes using <> is given priority 1
 - Includes using "" is given priority 2

It also disables putting the "main" file first (the .h/.hpp with the
same name as the .c/.cpp"

#5074
[ci skip]

.clang-format

@@ -7,6 +7,14 @@ AllowShortFunctionsOnASingleLine: Empty
 BreakBeforeBraces: Allman
 ColumnLimit: '128'
 Cpp11BracedListStyle: 'false'
+IncludeCategories:
+  - Regex:           '^"(\./)*common\.h"$'
+    Priority:        -1
+  - Regex:           '^<.*>$'
+    Priority:        1
+  - Regex:           '^".*"$'
+    Priority:        2
+IncludeIsMainRegex: 'false'
 IndentWidth: '4'
 PointerAlignment: Middle
 SortIncludes: 'true'