Enabled refine_MatMul to accept non Matrix arguments
Enabled refine_MatMul to accept non Matrix arguments

Fix for #11359
Previously, only is_Matrix arguments could be accepted by refine_MatMul
 which prevents testing of further assumptions. Hence the variable
`last` is set such a way that it is a Matrix.

jaimahajan1997/sympy,souravsingh/sympy,postvakje/sympy,skidzo/sympy,souravsingh/sympy,aktech/sympy,kaushik94/sympy,kaushik94/sympy,madan96/sympy,yashsharan/sympy,jaimahajan1997/sympy,kaushik94/sympy,skidzo/sympy,aktech/sympy,skidzo/sympy,jaimahajan1997/sympy,drufat/sympy,sampadsaha5/sympy,yashsharan/sympy,chaffra/sympy,aktech/sympy,chaffra/sympy,postvakje/sympy,drufat/sympy,madan96/sympy,sampadsaha5/sympy,souravsingh/sympy,drufat/sympy,postvakje/sympy,sampadsaha5/sympy,chaffra/sympy,madan96/sympy,yashsharan/sympy