ARM: VIXL32: Use 16-bit encoding for B(cond,...) where possible.

If conditional branch's target is known to be not far from branch
(within the range of 254 bytes), 16-bit encoding can be used.
However, we can't assume this by default for branches to a basic
block or a slow path; if we do and fail the range requirement,
veneer pool will be emitted.

Test: ART_USE_VIXL_ARM_BACKEND=true m test-art-host
Test: ART_USE_VIXL_ARM_BACKEND=true m test-art-target
Change-Id: I2fbe6d1a43bc2d1b54472c2c3fe05a575e5634f2