Pytorch MatMul Substitution

[itai-berman]

Pull Request Description:

Add substitution to support MatMul function & operator by doing Reshape->Split->2D MatMul->Stack->Reshape

Checklist before requesting a review:

• I set the appropriate labels on the pull request.
• I have added/updated the release note draft (if necessary).
• I have updated the documentation to reflect my changes (if necessary).
• All function and files are well documented.
• All function and classes have type hints.
• There is a licenses in all file.
• The function and variable names are informative.
• I have checked for code duplications.
• I have added new unittest (if necessary).

[elad-c]

mention is the substitution is inplace.