Fix Bh1-Bh2 swap bug in NRSur7dq4 when m1 < m2

Description

When m1 < m2, the NRSur7dq4 code previously did the following:

1. Swap the labels of the two BH, i.e. m1 <-> m2, chi1 <-> chi2.
2. Multiply the odd-m modes by -1 to undo this swap.

The assumption here is that the first step is only a rigid rotation by pi, and the second step undoes this rigid rotation.

However, the first step is only a rigid rotation if after the swap the in-plane spins are also rotated by pi. This is demonstrated here: https://git.ligo.org/waveforms/reviews/RemnantFits/wikis/home/label_swap_test

The previous code failed this test, as the in-plane spins were not rotated after the swap:

This is now fixed:

API Changes and Justification

Backwards Compatible Changes

• This change introduces no API changes
• This change adds new API calls

Backwards Incompatible Changes

• This change modifies an existing API
• This change removes an existing API

Review Status

This model is already reviewed: https://git.ligo.org/waveforms/reviews/nrsur7dq4/wikis/home This bug fix should not affect most PE runs as m1 < m2 is excluded in most cases anyway.