glslang doesn't apply `NoContraction` through struct constructors

Noticed while implementing a similar algorithm in ANGLE. Take the following shader:

```c
#version 450 core

float u;

struct S1
{
precise float f;
int i;
precise vec4 v;
mat4 m;
};

void main()
{
float f = u; // f is precise
int i = int(u);
vec4 v1 = vec4(u); // v1 is precise
vec4 v2 = vec4(u);

f += 1.0; // NoContraction

i--;
i--;

v1 *= 2.0; // NoContraction
v1 *= 2.0; // NoContraction
v1 *= 2.0; // NoContraction
v1 *= 2.0; // NoContraction

v2 /= 3.0;
v2 /= 3.0;
v2 /= 3.0;
v2 /= 3.0;
v2 /= 3.0;
v2 /= 3.0;
v2 /= 3.0;
v2 /= 3.0;
v2 /= 3.0;

S1 s = S1(f, i, v1, mat4(v2, v2, v2, v2));

gl_Position = vec4(s.f, float(s.i), s.v[0], s.m[0][0]);
}
```

The line that constructs S1 should propagate precise-ness to variables `f` and `v1`, making their calculation precise. glslang produces no `NoContraction` decorations. It's not for a lack of trying though, [there is code][1] that's supposed to do this.

[1]: https://github.com/KhronosGroup/glslang/blob/master/glslang/MachineIndependent/propagateNoContraction.cpp#L666