Add a sample outline shader (#9646)

I accidentally the whole thing

## References
* Heavily inspired by the original rasterbars shader.

## PR Checklist
* [x] Closes #9010

samples/PixelShaders/Outlines.hlsl

@@ -0,0 +1,66 @@
+// A minimal pixel shader that outlines text
+
+// The terminal graphics as a texture
+Texture2D shaderTexture;
+SamplerState samplerState;
+
+// Terminal settings such as the resolution of the texture
+cbuffer PixelShaderSettings {
+  // The number of seconds since the pixel shader was enabled
+  float  Time;
+  // UI Scale
+  float  Scale;
+  // Resolution of the shaderTexture
+  float2 Resolution;
+  // Background color as rgba
+  float4 Background;
+};
+
+// A pixel shader is a program that given a texture coordinate (tex) produces a color.
+// tex is an x,y tuple that ranges from 0,0 (top left) to 1,1 (bottom right).
+// Just ignore the pos parameter.
+float4 main(float4 pos : SV_POSITION, float2 tex : TEXCOORD) : SV_TARGET
+{
+    // Read the color value at the current texture coordinate (tex)
+    //  float4 is tuple of 4 floats, rgba
+    float4 color = shaderTexture.Sample(samplerState, tex);
+
+    // Read the color value at some offset, will be used as shadow. For the best
+    // effect, read the colors offset on the left, right, top, bottom of this
+    // fragment, as well as on the corners of this fragment.
+    //
+    // You could get away with fewer samples, but the resulting outlines will be
+    // blurrier.
+
+    //left, right, top, bottom:
+    float4 leftColor   = shaderTexture.Sample(samplerState, tex+1.0*Scale*float2( 1.0,  0.0)/Resolution.y);
+    float4 rightColor  = shaderTexture.Sample(samplerState, tex+1.0*Scale*float2(-1.0,  0.0)/Resolution.y);
+    float4 topColor    = shaderTexture.Sample(samplerState, tex+1.0*Scale*float2( 0.0,  1.0)/Resolution.y);
+    float4 bottomColor = shaderTexture.Sample(samplerState, tex+1.0*Scale*float2( 0.0, -1.0)/Resolution.y);
+
+    // Corners
+    float4 topLeftColor     = shaderTexture.Sample(samplerState, tex+1.0*Scale*float2( 1.0,  1.0)/Resolution.y);
+    float4 topRightColor    = shaderTexture.Sample(samplerState, tex+1.0*Scale*float2(-1.0,  1.0)/Resolution.y);
+    float4 bottomLeftColor  = shaderTexture.Sample(samplerState, tex+1.0*Scale*float2( 1.0, -1.0)/Resolution.y);
+    float4 bottomRightColor = shaderTexture.Sample(samplerState, tex+1.0*Scale*float2(-1.0, -1.0)/Resolution.y);
+
+
+    // Now, if any of those adjacent cells has text in it, then the *color vec4
+    // will have a non-zero .w (which is used for alpha). Use that alpha value
+    // to add some black to the current fragment.
+    //
+    // This will result in only coloring fragments adjacent to text, but leaving
+    // background images (for example) untouched.
+    float3 outlineColor = float3(0, 0, 0);
+    float4 result = color;
+    result = result + float4(outlineColor, leftColor.w);
+    result = result + float4(outlineColor, rightColor.w);
+    result = result + float4(outlineColor, topColor.w);
+    result = result + float4(outlineColor, bottomColor.w);
+
+    result = result + float4(outlineColor, topLeftColor.w);
+    result = result + float4(outlineColor, topRightColor.w);
+    result = result + float4(outlineColor, bottomLeftColor.w);
+    result = result + float4(outlineColor, bottomRightColor.w);
+    return result;
+}