[vm] Remove overlap between Function and FunctionType.

Previously there were several pieces of information shared between
both FunctionType and Function, mostly in the packed fields, but
named argument names were also kept in both places.

Now the FunctionType is the primary source for this information, with
the Function only keeping the names of positional arguments, which are
discarded in AOT snapshots.

This does mean extra work to access this information via the function
object, but for the most part, this information is only accessed in the
compiler or during dynamic lookups or checks in the runtime.

After adding the count of type parameters to the packed information
in FunctionType, the packed information has been split into two pieces:
one for parameter counts, another for type parameter counts. This
split does not increase the size of UntaggedFunctionType, as there
were 2 bytes available in the existing padding.

Changes on flutter gallery in release mode:

* ARM7 code size: total -0.91%, readonly -0.22%, isolate -4.32%
* ARM7 heap size: total -2.00%
* ARM8 code size: total -0.93%, readonly -0.22%, isolate -4.32%
* ARM8 heap size: total -2.12%

Changes on flutter gallery in release-sizeopt mode:

* ARM7 code size: total -0.24%, readonly -0.08%, isolate -1.49%
* ARM7 heap size: total -0.88%
* ARM8 code size: total -0.26%, readonly -0.11%, isolate -1.49%
* ARM8 heap size: total -1.01%

TEST=Refactoring, so existing tests.

Cq-Include-Trybots: luci.dart.try:vm-kernel-linux-debug-x64-try,vm-kernel-nnbd-linux-debug-x64-try,vm-kernel-precomp-linux-debug-x64-try,vm-kernel-precomp-nnbd-linux-debug-x64-try,vm-kernel-reload-linux-debug-x64-try,vm-kernel-reload-rollback-linux-debug-x64-try,vm-kernel-precomp-linux-debug-simarm_x64-try,vm-kernel-precomp-nnbd-linux-debug-simarm_x64-try,vm-kernel-linux-debug-ia32-try,vm-kernel-nnbd-linux-debug-ia32-try,vm-kernel-linux-release-simarm-try,vm-kernel-linux-release-simarm64-try,vm-kernel-precomp-linux-debug-simarm_x64-try,vm-kernel-precomp-linux-release-simarm-try,vm-kernel-precomp-linux-release-simarm64-try,vm-kernel-precomp-nnbd-linux-debug-simarm_x64-try,vm-kernel-precomp-nnbd-linux-release-simarm64-try
Change-Id: Ic4d59a7b4acca039a5647f9163e716f6019163f5
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/203241
Commit-Queue: Tess Strickland <sstrickl@google.com>
Reviewed-by: Ryan Macnak <rmacnak@google.com>
Reviewed-by: Martin Kustermann <kustermann@google.com>
Reviewed-by: Régis Crelier <regis@google.com>