Add shaders re-implemented in HLSL

These were written against the shaders at revision eddd724e7.
There have been changes made since then, which will need to be mirrored.

See `data/hlsl/README.md` for the current status of each sample.

data/hlsl/base/textoverlay.frag

@@ -0,0 +1,10 @@
+// Copyright 2020 Google LLC
+
+Texture2D textureFont : register(t0);
+SamplerState samplerFont : register(s0);
+
+float4 main([[vk::location(0)]]float2 inUV : TEXCOORD0) : SV_TARGET
+{
+	float color = textureFont.Sample(samplerFont, inUV).r;
+	return float4(color.xxx, 1.0);
+}