This CL changes for floats what https://chromium-review.googlesource.com/c/558964/
changed for doubles.

Original message:
On x86, signalling NaNs get converted to quiet NaNs when they get push
on the stack and popped again. This happens in the code generation for
arm, specifically for the vmov instruction with the immediate parameter.
This CL replaces the vmov function in assembler-arm to take the
immediate as a uint64_t instead of a double, to guarantee that the bit
pattern does not change even if the parameter is a signalling NaN.

New in this CL:
Although src/double.h existed already, src/float.h did not exist yet.
I created the file in this CL, and moved the classes Float32 and
Float64 there, which already existed in src/deoptimizer.h.

R=titzer@chromium.org, martyn.capewell@arm.com, v8-arm-ports@googlegroups.com

BUG=v8:6564

Change-Id: I6a3f1f154af9c8cd4bb8e7e856235d3eee5e9edd
Reviewed-on: https://chromium-review.googlesource.com/561009
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Martyn Capewell <martyn.capewell@arm.com>
Reviewed-by: Ben Titzer <titzer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46473}