Add ImDrawList UserCallback support

[Soreepeong]

Commits need to be edited after merging ImGuiScene#11 first.

When reviewing, the relevant commit is the third commit. Four commit is for example purposes; it is to be removed before merging.

Also, did the following:

• Add Dalamud.CorePlugin.json.
• Expose DeviceContext from UiBuilder.
• Expose DeviceNativePointer and DeviceContextNativePointer, due to SharpDX dependency types in Dalamud assembly not being exposed correctly to plugins, resulting in incompatible types across assemblies. Or, that's what I think what's going on, at least.

SamplerState Sampler : register(s0);
Texture2D Texture : register(t0);

struct PSInput {
    float4 position : SV_POSITION;
    float4 color : COLOR;
    float2 uv : TEXCOORD;
};

float4 main_ps(PSInput input) : SV_TARGET {
    const float4 color = Texture.Sample(Sampler, input.uv);
    switch (floor(input.uv.x)) {
        case 1: return float4(input.color.xyz, color.r);
        case 2: return float4(input.color.xyz, color.g);
        case 3: return float4(input.color.xyz, color.b);
        case 4: return float4(input.color.xyz, color.a);
        default: return input.color * color;
    }
}

test.fxc.zip