RELNOTES: This allows the use of '.' in variables (e.g. "hparams.parse('a.b=1.0'...

RELNOTES: This allows the use of '.' in variables (e.g. "hparams.parse('a.b=1.0')"), which would previously raise an error. This will correspond to an attribute name with an embedded '.' symbol (e.g. 'a.b'), which can only be accessed indirectly (e.g. through getattr and setattr).  To set this up the user will first need to explicitly add the variable to the hparam object (e.g. "hparams.add_hparam(name='a.b', value=0.0)").

NOTE: the use of '.' in variable names is now allowed, but it is not recommended.
PiperOrigin-RevId: 196278660