BLI: Refactor matrix types & functions to use templates

This patch implements the matrix types (i.e:float4x4) by making heavy
usage of templating. All matrix functions are now outside of the vector
classes (inside the blender::math namespace) and are not vector size
dependent for the most part.

###Motivations
The goal/motivations of this rewrite are the same as the Vector C++ API (D13791):
- Template everything for making it work with any types and avoid code duplication.
- Use functional style instead of Object Oriented function call to allow a simple compatibility layer with GLSL syntax (see T103026 for more details).
- Allow most convenient constructor syntax and accessors (array subscript `matrix[c][r]`, or component alias `matrix.y.z`).
- Make it cover all features the current C API supports for adoption.
- Keep compilation time and debug performance somehow acceptable.

###Consideration:
- The new `MatView` class can be generated by `my_float.view<NumCol, NumRow, StartCol, StartRow>()` (with the last 2 being optionnal). This one allows modifying parts of the source matrix in place. It isn't pretty and duplicates a lot of code, but it is needed mainly to replace `normalize_m4`. At least I think it is a good starting point that can refined further.
- An exhaustive list of missing `BLI_math_matrix.h` functions from the new API can be found here P3373.
- This adds new Rotation types in order to have a clean API. This will be extended when we port the full Rotation API. The types are made so that they don't allow implicit down-casting to their vector representation.
- Some functions make direct use of the Eigen library, bypassing the Eigen C API defined in `intern/eigen`. Its use is contained inside `math_matrix.cc`. There is conflicting opinion wether we should use it more so I contained its usage to almost the tasks as in the C API for now.

Reviewed By: sergey, JacquesLucke, HooglyBoogly, Severin, brecht
Differential Revision: https://developer.blender.org/D16625

tests/gtests/testing/testing.h

@@ -42,6 +42,12 @@ const std::string &flags_test_release_dir(); /* bin/{blender version} in the bui
   } \
   (void)0
 
+#define EXPECT_M2_NEAR(a, b, eps) \
+  do { \
+    EXPECT_V2_NEAR(a[0], b[0], eps); \
+    EXPECT_V2_NEAR(a[1], b[1], eps); \
+  } while (false);
+
 #define EXPECT_M3_NEAR(a, b, eps) \
   do { \
     EXPECT_V3_NEAR(a[0], b[0], eps); \