Offset tris from fragments for triangle tests

Offset tris from fragments for triangle tests

At some render resolutions, these tests can rely on the outcome of a
rasterizer tie-break. Since such behavior is left unspecified, we
offset the generated triangles slightly to ensure that they reliably
hit (or miss) the fragment locations we expect them to.

Affects:
KHR-GLES31.core.draw_indirect.basic-mode-drawArrays-triangle_strip_adjacency
KHR-GLES31.core.draw_indirect.basic-mode-drawArrays-triangles_adjacency
KHR-GLES31.core.draw_indirect.basic-mode-drawElements-triangle_strip_adjacency
KHR-GLES31.core.draw_indirect.basic-mode-drawElements-triangles_adjacency

Components: OpenGL ES

VK-GL-CTS issue: 2522

Change-Id: I63ab56dba99b5e6f6369aa4fd8b4538c9d01d874