feat: high-level implementations for Positional Embeddings #4066

Job	Run time
test (1.10, ubuntu-latest, core_layers)	17m 44s
test (1.10, ubuntu-latest, normalize_layers)	20m 30s
test (1.10, ubuntu-latest, recurrent_layers)	28m 15s
test (1.10, ubuntu-latest, autodiff)	50m 33s
test (1.10, ubuntu-latest, misc)	33m 8s
test (1.10, ubuntu-latest, reactant)	8m 45s
test (1, ubuntu-latest, core_layers)	21m 20s
test (1, ubuntu-latest, normalize_layers)	25m 31s
test (1, ubuntu-latest, recurrent_layers)	35m 25s
test (1, ubuntu-latest, autodiff)	36m 53s
test (1, ubuntu-latest, misc)	34m 0s
test (1, ubuntu-latest, reactant)	9m 1s
downgrade (core_layers)	21m 38s
downgrade (normalize_layers)	24m 4s
downgrade (recurrent_layers)	37m 24s
downgrade (autodiff)	54m 25s
downgrade (misc)	33m 42s
downgrade (reactant)	5m 44s
	8h 18m 2s

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