feat: Add translateByVector2 method to Matrix4

[luanpotter]

Before the deprecation of the dynamic translate method, since the z variable had default value of 0, you could translate by a vector two by doing:

matrix4.translate(vector2.x, vector2.y)

Here is an example "in the wild" of such usage.

With the new methods, this becomes even less ergonomic, as it would require either calling translateByDouble with 2 extra parameters, or converting the Vector2 to a Vector3.

So I propose we introduce a translateByVector2 which behaves exactly as translate(x, y) would before.

[luanpotter]

note: I shifted the variable names a bit here to make it match some sort of logic with the new names, but please lmk if there is a preferred naming convention.

tbh this test feels like two tests in one but I don't want to change the structure too much.

[coveralls]

coverage: 26.711% (+0.009%) from 26.702%
when pulling 6017083 on luanpotter:luan.translateByVector2
into 3939545 on google:master.

[spydon]

@kevmoo could we have a review of this one? :)

[spydon]

@luanpotter tool/generate_vector_math_64.dart needs to be run so that it generates the vector_math_64 file too.