Use smaller triangles in triangle_vertex.clip_three

Use smaller triangles in triangle_vertex.clip_three

A few tests in clipping.triangle_vertex.clip_three generate triangles
that extend over 2^22 units in NDC outside viewport (something real
content is never expected to contain). Clipping these is not something
older ES2-only GPUs are necessarily expected to do accurately and might
come with prohibitive performance cost. This change limits size of those
triangles to a more reasonable value.

Bug: 27533503
Change-Id: Ic571b9d79db2c40652e96f4fc6a567fcfa7dcee3