Improve performance of `seqChild/4`
Improve performance of `seqChild/4`

Gets rid of the following bad join-order
```
[2021-06-29 09:40:44] (5s) Starting to evaluate predicate RegExpTreeView::seqChild#fffff#reorder_0_1_2_4_3/5@i2#fe59dz (iteration 2)
[2021-06-29 09:46:34] (354s) Tuple counts for RegExpTreeView::seqChild#fffff#reorder_0_1_2_4_3/5@i2#fe59dz:
                      222277     ~0%     {5} r1 = SCAN RegExpTreeView::RegExpTerm#ffff#prev_delta OUTPUT In.1 're', In.2 'start', In.3, 0, In.0 'result'
                      207749     ~3%     {4} r2 = JOIN r1 WITH ParseRegExp::RegExp::item_dispred#fff ON FIRST 3 OUTPUT Lhs.0 're', Lhs.1 'start', 0, Lhs.4 'result'
                      11636      ~2%     {5} r3 = JOIN r2 WITH ParseRegExp::RegExp::sequence_dispred#fff ON FIRST 2 OUTPUT 0, Lhs.3 'result', Lhs.0 're', Lhs.1 'start', Rhs.2 'end'

                      222277     ~0%     {4} r4 = SCAN RegExpTreeView::RegExpTerm#ffff#prev_delta OUTPUT In.1 're', In.2 'start', In.3, In.0 'result'
                      207749     ~0%     {3} r5 = JOIN r4 WITH ParseRegExp::RegExp::item_dispred#fff ON FIRST 3 OUTPUT Lhs.1, Lhs.3 'result', Lhs.0 're'
                      902017671  ~2%     {3} r6 = JOIN r5 WITH RegExpTreeView::RegExpTerm#ffff#reorder_3_0_1_2#prev ON FIRST 1 OUTPUT Lhs.2 're', Lhs.1 'result', Rhs.1
                      1193975963 ~2%     {5} r7 = JOIN r6 WITH ParseRegExp::RegExp::sequence_dispred#fff ON FIRST 1 OUTPUT Lhs.0 're', Rhs.1, Rhs.2 'end', Lhs.2, Lhs.1 'result'
                      0          ~0%     {6} r8 = JOIN r7 WITH RegExpTreeView::seqChild#fffff#reorder_0_1_2_4_3#prev ON FIRST 4 OUTPUT Lhs.4 'result', Lhs.0 're', Lhs.1 'start', Lhs.2 'end', Rhs.4 're', (1 + Rhs.4 're')
                      0          ~0%     {6} r9 = SELECT r8 ON In.5 'i' > 0
                      0          ~0%     {5} r10 = SCAN r9 OUTPUT In.5 'i', In.0 'result', In.1 're', In.2 'start', In.3 'end'

                      11636      ~2%     {5} r11 = r3 UNION r10

                      222277     ~3%     {2} r12 = SCAN RegExpTreeView::RegExpTerm#ffff#prev_delta OUTPUT In.3, In.0 'result'
                      961948702  ~4%     {5} r13 = JOIN r12 WITH RegExpTreeView::RegExpTerm#ffff#reorder_2_1_0_3#prev ON FIRST 1 OUTPUT Rhs.1 're', Lhs.0, Rhs.3, Lhs.1, Rhs.2 'result'
                      902017671  ~0%     {3} r14 = JOIN r13 WITH ParseRegExp::RegExp::item_dispred#fff ON FIRST 3 OUTPUT Lhs.0 're', Lhs.3, Lhs.4 'result'
                      1193975963 ~2%     {5} r15 = JOIN r14 WITH ParseRegExp::RegExp::sequence_dispred#fff ON FIRST 1 OUTPUT Lhs.0 're', Rhs.1, Rhs.2 'end', Lhs.1, Lhs.2 'result'
                      0          ~0%     {6} r16 = JOIN r15 WITH RegExpTreeView::seqChild#fffff#reorder_0_1_2_4_3#prev ON FIRST 4 OUTPUT Lhs.4 'result', Lhs.0 're', Lhs.1 'start', Lhs.2 'end', Rhs.4 're', (1 + Rhs.4 're')
                      0          ~0%     {6} r17 = SELECT r16 ON In.5 'i' > 0
                      0          ~0%     {5} r18 = SCAN r17 OUTPUT In.5 'i', In.0 'result', In.1 're', In.2 'start', In.3 'end'

                      0          ~0%     {5} r19 = SCAN RegExpTreeView::seqChild#fffff#reorder_0_1_2_4_3#prev_delta OUTPUT In.0 're', In.1 'start', In.2 'end', In.4, In.3
                      0          ~0%     {6} r20 = JOIN r19 WITH ParseRegExp::RegExp::sequence_dispred#fff ON FIRST 3 OUTPUT Lhs.0 're', Lhs.1 'start', Lhs.2 'end', Lhs.3, Lhs.4, (1 + Lhs.3)
                      0          ~0%     {6} r21 = SELECT r20 ON In.5 'i' > 0
                      0          ~0%     {5} r22 = SCAN r21 OUTPUT In.4, In.0 're', In.1 'start', In.2 'end', In.5 'i'
                      0          ~0%     {5} r23 = JOIN r22 WITH RegExpTreeView::RegExpTerm#ffff#prev ON FIRST 1 OUTPUT Rhs.3, Lhs.1 're', Lhs.2 'start', Lhs.3 'end', Lhs.4 'i'
                      0          ~0%     {7} r24 = JOIN r23 WITH RegExpTreeView::RegExpTerm#ffff#reorder_2_1_0_3#prev ON FIRST 2 OUTPUT Lhs.1 're', Lhs.0, Rhs.3, Lhs.2 'start', Lhs.3 'end', Lhs.4 'i', Rhs.2 'result'
                      0          ~0%     {5} r25 = JOIN r24 WITH ParseRegExp::RegExp::item_dispred#fff ON FIRST 3 OUTPUT Lhs.5 'i', Lhs.6 'result', Lhs.0 're', Lhs.3 'start', Lhs.4 'end'

                      0          ~0%     {5} r26 = r18 UNION r25
                      11636      ~2%     {5} r27 = r11 UNION r26
                      11636      ~2%     {5} r28 = r27 AND NOT RegExpTreeView::seqChild#fffff#reorder_0_1_2_4_3#prev(Lhs.2 're', Lhs.3 'start', Lhs.4 'end', Lhs.1 'result', Lhs.0 'i')
                      11636      ~0%     {5} r29 = SCAN r28 OUTPUT In.2 're', In.3 'start', In.4 'end', In.1 'result', In.0 'i'
                                         return r29
```

github/codeql,github/codeql,github/codeql,github/codeql,github/codeql,github/codeql,github/codeql,github/codeql,github/codeql,github/codeql,github/codeql,github/codeql,github/codeql,github/codeql,github/codeql