Use heap to allocate PatternMatch to avoid potential stack overflow

Use heap to allocate PatternMatch to avoid potential stack overflow

When apt-cache search with many args (> 130) is given the allocation
of PatternMatch on the stack may fail resulting in a segmentation
fault. By using the heap the max size is much bigger and we also
get a bad_alloc expection instead of a segfault (which we can catch
*if* this ever becomes a pratical problem). No test for the crash
as its not reproducable with the MALLOC_ settings in framework.

Closes: 759612