Handle scalar real HLO instructions from tf.lgamma and tf.digamma

Currently, the XLA tf.lgamma op doesn't behave the same way as the standard
tf.lgamma with certain real values because the log of a negative number is
taken.

Added regression tests for tf.lgamma operating on a scalar and added cases that
previously resulted in NaNs when using the reflection formula.

PiperOrigin-RevId: 209443312