Flatten uniform arrays

This checkin adds a --flatten-uniform-arrays option which can break
uniform arrays of samplers, textures, or UBOs up into individual
scalars named (e.g) myarray[0], myarray[1], etc.  These appear as
individual linkage objects.

Code notes:

- shouldFlatten internally calls shouldFlattenIO, and shouldFlattenUniform,
  but is the only flattening query directly called.

- flattenVariable will handle structs or arrays (but not yet arrayed structs;
  this is tested an an error is generated).

- There's some error checking around unhandled situations.  E.g, flattening
  uniform arrays with initializer lists is not implemented.

- This piggybacks on as much of the existing mechanism for struct flattening
  as it can.  E.g, it uses the same flattenMap, and the same
  flattenAccess() method.

- handleAssign() has been generalized to cope with either structs or arrays.

- Extended test infrastructure to test flattening ability.

Test/hlsl.array.flatten.frag

@@ -0,0 +1,38 @@
+
+// uniform Texture1D g_tex3[3][2];  // TODO: legal in HLSL, but we don't handle it yet.
+
+uniform Texture1D g_tex[3];
+uniform Texture1D g_tex_explicit[3] : register(t1);
+
+SamplerState g_samp[3];
+SamplerState g_samp_explicit[3] : register(s5);
+
+uniform float3x3 g_mats[4];
+uniform float3x3 g_mats_explicit[4] : register(b10);
+uniform float g_floats[4];
+
+// uniform float g_floats[4] = { 10, 11, 12, 13 };  // TODO: ... add when initializer lists can be flattened.
+
+float4 TestFn1()
+{
+    return g_tex[1].Sample(g_samp[1], 0.2);
+}
+
+float4 TestFn2(Texture1D l_tex[3], SamplerState l_samp[3])
+{
+    return l_tex[2].Sample(l_samp[2], 0.2);
+}
+
+int not_flattened_a[5] = { 1, 2, 3, 4, 5 };
+
+struct PS_OUTPUT { float4 color : SV_Target0; };
+
+void main(out PS_OUTPUT ps_output)
+{
+    // test flattening for local assignment initialization
+    SamplerState local_sampler_array[3] = g_samp;
+    Texture1D local_texture_array[3]    = g_tex;
+    float local_float_array[4]          = g_floats;
+
+    ps_output.color = TestFn1() + TestFn2(g_tex, g_samp);
+}