Fix passing struct with four floats in registers via reflection (#7716)

Fix passing struct with four floats in registers via reflection (#7716)

This change fixes a bug in the code that copies a struct into the transition
frame. When it contains four floats, the first two are put to the right place,
but the following two are placed to an address that's offset by 8 instead of
by 16.

It also adds regression test for this problem as Pri 1 test.