This adds support to the following type of shader code, where an array
constructor is used as a source of assignment:

float a[3];
a = float[3](0.0, 1.0, 2.0);

The assignment gets replaced in the HLSL code by a function call where
the array is an out parameter and the constructor parameters are regular
parameters.

Constructors cannot yet be used in initializers.

With this change in place, some of the relevant dEQP tests start passing.

TEST=dEQP-GLES3.functional.shaders.arrays.constructor.*
BUG=angleproject:941

Change-Id: I13ed603c02a30d9f9950a61c4d562ae9fac058ec
Reviewed-on: https://chromium-review.googlesource.com/263403Reviewed-by: Olli Etuaho <oetuaho@nvidia.com>
Tested-by: Olli Etuaho <oetuaho@nvidia.com>