Angular observables in B0->D*lnu

[Jorge-Alda]

Belle-II has recently published (arXiv:2308.02023) some angular measurements in $B^0\to D^{*-} \mu^+ \bar{\nu}_\mu$ and $B^0\to D^{*-} e^+ \bar{\nu}_e$ decays that were not implemented in flavio.

We have adapted the code used to calculate the angular observables in $B\to V\ell^+\ell^-$. All the differential and binned observables are implemented for all the available processes ($B^0\to D^{*-}$, $B^+\to D^{*0}$, $B^0\to\rho^+$, $B^+\to\rho^0$, $B^+\to\omega$ and $B_s\to K^{*-}$ and all three leptons). The LFU differences $D_{\mu e}$ are only implemented for the $B^0\to D^{*-}$ process in the observables measured at Belle-II: $A_\mathrm{FB}$, $S_3$, $S_5$, $S_7$ and $S_9$, although we could extend it to other observables and processes if needed.

[peterstangl]

Thank you very much for this PR! I hope to find the time soon to review your implementation in more detail!

[peterstangl]

Btw, the test seems to fail since the particle package has removed the 2018 data file in their latest version (Issue #237).