Added support for constants in shader case and array size declaration

[Chaosus]

Allows using const variables at case labels in switch expression of the shader eg.

shader_type spatial;

const int test = 0;

void fragment() {
	const int t = 0;
	switch(t) {
		case test:
			ALBEDO = vec3(1, 0, 0);
			break;
	}
}

---

Fixed array initialization using constants:

const int COUNT = 2; // OK

void fragment()
{
  float test[COUNT];

   const int COUNT2 = 2; // OK

   float test2[COUNT2];
}
const int COUNT = 0; // ERROR (invalid size)

void fragment()
{
  float test[COUNT];

   int COUNT2 = 2; // ERROR (non-const)

   float test2[COUNT2];
}

Fix #44145
Fix #44422

[Chaosus]

Combined with #44151 (they are using the same code parts)

[clayjohn]

I don't understand it all, but nothing jumped out as problematic and you're the expert here so let's go ahead.