Fix circular dependency in fixed_function.h (#350)

* Include fixed_function at top of test file

This will trigger compilation errors under the current setup due
to the recursive dependency; moving it here should allow us to
detect if this issue rears its head again in the future.

* Limit inclusion of functional.h by utility.h

A circular dependency was forming when function_detail.h was
included ahead of function.h, which could occur if a user included
fixed_function.h prior to functional.h.

As utility.h only requires the type traits for
eastl::reference_wrapper, this limits the inclusion to only
attempting to pull them in instead of the entirety of functional.h.

This may break users who depend upon utility.h pulling in functional.h.

* Reorder test includes per review comments

Added a link to the issue to document the ordering as well, so
it's a bit clearer for anyone 3 years down the line.

include/EASTL/utility.h

@@ -10,7 +10,7 @@
 #include <EASTL/internal/config.h>
 #include <EASTL/type_traits.h>
 #include <EASTL/iterator.h>
-#include <EASTL/functional.h>
+#include <EASTL/internal/functional_base.h>
 #include <EASTL/internal/move_help.h>
 #include <EABase/eahave.h>
 

test/source/TestFixedFunction.cpp

@@ -4,8 +4,12 @@
 
 #include <EABase/eabase.h>
 #include <EAAssert/eaassert.h>
-#include "EASTLTest.h"
+
+// Included prior to EASTLTest.h to guard against the following bug resurfacing:
+// https://github.com/electronicarts/EASTL/issues/275
 #include <EASTL/fixed_function.h>
+
+#include "EASTLTest.h"
 #include <EASTL/numeric.h>
 
 EA_DISABLE_ALL_VC_WARNINGS()