Exercise subclass of TransformerEncoderLayer (#105297)
Summary: Exercise subclass of TransformerEncoderLayer
Additional unit tests for change in #102045 to show correct e2e operation (cf. issue #100188)
Also: remove batch_first from list of TS module constants where it is not used to resolve torchscripting warning
Test Plan: saqndcastle, github
Differential Revision: D47503004
Pull Request resolved: https://github.com/pytorch/pytorch/pull/105297
Approved by: https://github.com/davidberard98
