[mlir][tosa] Add folders for trivial tosa operation cases

Some folding cases are trivial to fold away, specifically no-op cases where
an operation's input and output are the same. Canonicalizing these away
removes unneeded operations.

The current version includes tensor cast operations to resolve shape
discreprencies that occur when an operation's result type differs from the
input type. These are resolved during a tosa shape propagation pass.

Reviewed By: NatashaKnk

Differential Revision: https://reviews.llvm.org/D107321