[Relax] Support `input_axis_separator` to allow 2D to 1D conversion

[abhikran-quic]

• Introduce input_axis_separator in relax.transform_layout op for 2D input buffer to allow conversion of 2D buffers to 1D buffers. The conversion from 2D->1D is handled while lowering of transform_layout operator.
• This is needed because once the tensor is converted into 2D via axis_separator, the input_axis_separator helps in identifying the buffers with 2 dimensions especially when the conversion is needed to 1D operation.
• Also introducing support for input_axis_separator in AlterOpImpl pass.

[abhikran-quic]

cc: @Lunderberg , @tqchen

[abhikran-quic]

@tvm-bot rerun

[quic-sanirudh]

Thanks @abhikran-quic @Lunderberg

[abhikran-quic]

Thank you @Lunderberg, @quic-sanirudh !