Revert "[TableGen] Use heap allocated arrays instead of vectors for...

Revert "[TableGen] Use heap allocated arrays instead of vectors for TreePatternNode::Types and ResultPerm. NFC"

While working on DAGISelMatcherEmitter I've hit several runtime errors
caused by accessing TreePatternNode::Types out of bounds. These were
difficult to debug because the switch from std::vector to unique_ptr
removes bounds checking.

I don't think the slight reduction in class size is worth the extra
debugging and memory safety problems, so I suggest we revert this.

This reverts commit d34125a1.

Differential Revision: https://reviews.llvm.org/D154781