CLN/PERF: .get_loc on float with integer coercion

[jreback]

xref: #12370

This should be done inside index.pyx

if the lookup fails and if its a non-float index, then coerce to int, and if its the same
lookup again.

[toobaz]

I think this is fixed:

In [2]: idx = pd.Index([1, 2, 3])                                                                                                                             

In [3]: idx.get_loc(2.)                                                                                                                                       
Out[3]: 1