Similar to previous tests, vpgatherqq and vgatherqpd are equivalent
instructions. So the tests are the same with the mnemonic changed.
This adds tests for an additional two sets of instructions. Getting us
full coverage of all eight instructions if we include the tests from
PR #3167 and #3166
Tests the same things as described in #3165
In addition, since these tests use 64-bit indices for address
calculation, we can easily generate and indice vector that tests
overflow. So every test at every displacement ALSO gains an additional
overflow test to ensure correct behaviour around pointer overflow
calculation.
