Change the precision of size and uSize from mediumP to highP

Change the precision of size and uSize from mediumP to highP

When I checked the value of uSize and size set in the application, the
multiplication of these values could result in INF number if shader uses
mediump (fp16).

To avoid this problem, i change the precision of size and uSize from mediumP to highP

Change-Id: Iaa3e6f4427cfbf82a2ca59f0c5628f746ebdbb80