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/distancefieldfonts/sdf.frag

@@ -0,0 +1,30 @@
+// Copyright 2020 Google LLC
+
+Texture2D textureColor : register(t1);
+SamplerState samplerColor : register(s1);
+
+struct UBO
+{
+	float4 outlineColor;
+	float outlineWidth;
+	float outline;
+};
+
+cbuffer ubo : register(b2) { UBO ubo; }
+
+float4 main([[vk::location(0)]] float2 inUV : TEXCOORD0) : SV_TARGET
+{
+    float dist = textureColor.Sample(samplerColor, inUV).a;
+    float smoothWidth = fwidth(dist);
+    float alpha = smoothstep(0.5 - smoothWidth, 0.5 + smoothWidth, dist);
+	float3 rgb = alpha.xxx;
+
+	if (ubo.outline > 0.0)
+	{
+		float w = 1.0 - ubo.outlineWidth;
+		alpha = smoothstep(w - smoothWidth, w + smoothWidth, dist);
+        rgb += lerp(alpha.xxx, ubo.outlineColor.rgb, alpha);
+    }
+
+    return float4(rgb, alpha);
+}