Supports flexible config for mimic fisheye via drawBitmapMesh.

Original logic applies a 4x6 mesh for the fisheye effect.
Due to the mesh width is an integer, the ramp width cannot be adjusted,
instead, it is calculated based on the zoom and mesh width.
e.g. zoom = 1.5, mesh width = 4, the ramp width must be 0.125x of width.
That causes the inflexibility of adjusting the ramp width for potential
UX experiments.

This cl breaks the original pixel copied bitmap into 3 parts.
 - For the middle part, it just be drew scaled to the middle of magnifier.
 - For the left/right parts, it applies a 1x6 mesh to mimic the fisheye.
Because the mesh only applies the left/right parts, the ramp width can
be configured separately.

Test: m -j & manually tested.
Bug: 148763951
Change-Id: I7afe7e4b8d006b2b3a46513eadfea9fa8bf0515f