Test cases for the layers

[soran-ghaderi]

Test cases for the following layers:

• AddNorm #65
• MultiHeadAttention #64
• DotProductAttention #67
• [Tests] TransformerEncoder #100
• [tests] TransformerEncoderBlock #95
• TransformerDecoder
• [tests] TransformerDecoderBlock #96
• PositionalEncoding #70
• PositionwiseFFN #82

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