compiler: Fix harmless need_heap error for Maps

Need heap for maps is zero and fall through is also zero.
compiler: Refactor Map pairs aliasing
compiler: Properly support Map aliasing

Matching of type:

    #{K := V1} = #{K := V2} = M,

Will alias (coalesce) to

    #{K := V1 = V2} = M.
compiler: Update test for Maps aliasing