[Mosaic:TPU] Have VectorLayout::join handle fully replicated layouts and fix bug in infer-vector-layout elementwise rule
Consider the case where input layouts are
#tpu.vpad<"32,{*,*},(8,128),-1">
#tpu.vpad<"32,{*,0},(8,128)">
in this case we would have previously assigned the second layout, but that is incorrect because the true 2nd minor dimension is not known to be replicated for the first input
PiperOrigin-RevId: 810776770