Update isel pattern with 16bit types to use vgp16 in true16 mode. This
stop isel from generating illegal `vgpr32 = copy vpgr16`

This includes fcopysign, scalar_to_vector and i1 trunc. Updated lit test
and added a few mir tests.

Stacking up these changes in one patch as I realized that doing these
seperately could lead to unexpected failures in between.

When a node is picked, we should reset its next cluster candidate to
null before releasing its successors/predecessors.

This is a NFC patch.

This patch run a bulk update on CodeGen tests that are impacted by the
true16 features. This patch applies:
1. duplicate GFX11plus runlines and apply them with
"+mattr=+real-true16" and "+mattr=-real-true16"
2. update the test with the update script

For some GISEL runlines, the current CodeGen do not fully support the
true16 version. Still update the runlines, but comment out the failing
one, and added a "FIXME-TRUE16" comment to that test for easier
tracking. These test will be fixed in the following patches.

This is in a transition state that we support both
"+real-true16/-real-true16" in our code base. We plan to move to
"+real-true16" as default, and finally remove "-real-true16" mode and
test lines.

This reverts commit ca33649abe5fad93c57afef54e43ed9b3249cd86.

This reverts commit e215a1e27d84adad2635a52393621eb4fa439dc9 as it broke both
hip and openmp buildbots.

MSG_DEALLOC_VGPRS slows down very small waveslot limited kernels. It's
been identified this message is only really needed for VGPR limited
kernels. A kernel becomes VGPR limited if a total number of VGPRs per
SIMD / number of used VGPRs is more than a number of wave slots.

For targets that support xnack replay feature (gfx8+), the
multi-dword scalar loads shouldn't clobber any register that
holds the src address. The constrained version of the scalar
loads have the early clobber flag attached to the dst operand
to restrict RA from re-allocating any of the src regs for its
dst operand.

Consider the constrained multi-dword loads while merging
individual loads to a single multi-dword load.

This reverts commit adaff46d087799072438dd744b038e6fd50a2d78.

Drop the -O3 checks from default-attributes.hip. I don't know why they
are different on some bots but reverting this is far too disruptive.