HLSL: allow implicit array sizing.

In HLSL array sizes need not be provided explicitly in all circumstances.
For example, this is valid (note no number between the [ ]):

  // no explicit array size
  uniform float g_array[] = { 1, 2, 3, 4, 5 };

This PR does not attempt to validate most invalid cases.

A new test is added to verify the resulting linker objects.

Test/hlsl.array.implicit-size.frag

@@ -0,0 +1,31 @@
+
+// implicit sized array
+uniform float g_array [ ] = { 1, 2, 3, 4, 5 };
+
+// Unused implicit sized array
+uniform float g_array_unused [ ] = { 1, 2, 3, 4, 5, 6, 7 };
+
+// Test implicit size arrayed structs
+uniform struct mystruct {
+    int i;
+    float f;
+} g_mystruct[] = {
+    { 1, 2.0 },
+    { 3, 4.0 },
+};
+
+struct PS_OUTPUT { float4 color : SV_Target0; };
+
+// INVALID: implicit size requires an initializer expression.
+// uniform float bad[];
+
+// INVALID: function parameters cannot be implicitly sized
+// void BadFunction(int a[]) { }
+
+void main(out PS_OUTPUT ps_output)
+{
+    // implicit sized local array
+    float l_array[] = { 1, 2, 3 };
+
+    ps_output.color = g_array[0] + g_array[4] + l_array[1] + g_mystruct[0].f + g_array[idx];
+}