refactor: Improve ordering of headers with clang-format (#5343)

Removes all manual header groupings from source and header files by leveraging clang-format options.

.clang-format

@@ -44,6 +44,7 @@ DerivePointerAlignment: false
 DisableFormat:   false
 ExperimentalAutoDetectBinPacking: false
 ForEachMacros:   [ Q_FOREACH,  BOOST_FOREACH ]
+IncludeBlocks:   Regroup
 IncludeCategories:
   - Regex:           '^<(test)/'
     Priority:        0
@@ -53,8 +54,12 @@ IncludeCategories:
     Priority:        2
   - Regex:           '^<(boost)/'
     Priority:        3
-  - Regex:           '.*'
+  - Regex:           '^.*/'
     Priority:        4
+  - Regex:           '^.*\.h'
+    Priority:        5
+  - Regex:           '.*'
+    Priority:        6
 IncludeIsMainRegex: '$'
 IndentCaseLabels: true
 IndentFunctionDeclarationAfterType: false