Fix wrong result of interpolateAtSample/AtOffset
Fix wrong result of interpolateAtSample/AtOffset

- RootCause:Coefficient I/w and J/w are multiplied by 1/w which gives an incorrect barycentric coord
- Solution: Add a rcp instruction to get w and use it to replace 1/w

googlestadia/llpc,GPUOpen-Drivers/llpc,googlestadia/llpc,GPUOpen-Drivers/llpc,googlestadia/llpc,googlestadia/llpc,GPUOpen-Drivers/llpc,GPUOpen-Drivers/llpc,googlestadia/llpc,GPUOpen-Drivers/llpc