[unity] Fixed SkeletonGraphic shader texcoord precision issue. Closes #2892.

spine-unity/Assets/Spine/Runtime/spine-unity/Shaders/SkeletonGraphic/CGIncludes/Spine-SkeletonGraphic-NormalPass.cginc

@@ -17,7 +17,7 @@ struct VertexInput {
 struct VertexOutput {
 	float4 vertex   : SV_POSITION;
 	fixed4 color    : COLOR;
-	half2 texcoord  : TEXCOORD0;
+	float2 texcoord  : TEXCOORD0;
 	float4 worldPosition : TEXCOORD1;
 	UNITY_VERTEX_OUTPUT_STEREO
 };

spine-unity/Assets/Spine/Runtime/spine-unity/Shaders/SkeletonGraphic/CGIncludes/Spine-SkeletonGraphic-TintBlack-NormalPass.cginc

@@ -19,7 +19,7 @@ struct VertexInput {
 struct VertexOutput {
 	float4 vertex   : SV_POSITION;
 	half4 color    : COLOR;
-	half2 texcoord  : TEXCOORD0;
+	float2 texcoord  : TEXCOORD0;
 	float4 darkColor : TEXCOORD1;
 	float4 worldPosition : TEXCOORD2;
 #ifdef _CANVAS_GROUP_COMPATIBLE