Do not create `MethodType` during early init...

... when interpreting `VarHandle` invoke-polymorphic.

Use `VariableSizedHandleScope` as a raw method type that can
be converted to the managed `MethodType` when desires but
can also be used directly without the conversion. Add helper
templates that facilitate using either the raw method type
or the managed `MethodType` easily by templated code.

Change `VarHandleInvokeAccessorWithConversions()` to avoid
allocating the `MethodType` (avoid unnecessary work).

Change `VarHandle` invokes in the interpreter to avoid
allocating the `MethodType` when the `ThreadLocalRandom`
is not initialized. This can avoid circular initialization
when we reland
    https://android-review.googlesource.com/2769639 .

Test: m test-art-host-gtest
Test: testrunner.py --host --optimizing
Bug: 297147201
Change-Id: I6a9372543a547366b28e5bf49d15d6140a75f770