Fix subpixel precision for line geometry generation
Fix subpixel precision for line geometry generation

Line geometry generation for rasterization tests wasn't taking the HW
subPixelPrecisionBits limit into account. Modified the triangle creation
routines to round those coordinates down to the driver provided
precision.

Affects:

dEQP-VK.rasterization.*line*
dEQP-GLES*.functional.rasterization.*line*

Components: Framework

VK-GL-CTS issue: 1274

Change-Id: I54af2f9606372bead2a8c7238588374101f80e55

KhronosGroup/VK-GL-CTS,KhronosGroup/Vulkan-CTS,googlestadia/VK-GL-CTS,KhronosGroup/Vulkan-CTS,KhronosGroup/VK-GL-CTS,KhronosGroup/VK-GL-CTS,KhronosGroup/Vulkan-CTS,KhronosGroup/VK-GL-CTS,KhronosGroup/VK-GL-CTS,googlestadia/VK-GL-CTS,googlestadia/VK-GL-CTS,KhronosGroup/Vulkan-CTS,KhronosGroup/Vulkan-CTS,KhronosGroup/VK-GL-CTS,googlestadia/VK-GL-CTS,googlestadia/VK-GL-CTS,KhronosGroup/Vulkan-CTS,googlestadia/VK-GL-CTS