The `JoinOrderBuilder` builds reordered join plans from the bottom up.
It expects filters to be pushed down as far as possible at each step, and
that transitive closure has been calculated over Inner Join equality filters
(e.g. `a=b` and `b=c` => `a=c`). It also reuses the original matched joins
when possible to avoid duplicate work by adding to the original memo groups.

This could previously cause filters to be dropped in the case when the
original join tree did not compute transitive closure and push filters down
as far as possible. More specifically, the `JoinOrderBuilder` could add new
reordered joins with new filters synthesized and pushed down as far as possible
to an original memo group that didn't have one of those filters. Subsequent
joins would then expect the filter to be part of the memo group, and so it
wouldn't be added later on in the plan. In the rare case when the expression
without the filter was chosen, this could manifest as a dropped filter in the
final plan. This was rare because dropping a filter usually does not produce
a lower-cost plan.

As an example, take this original join tree:
```
(xy join ab on true) join uv on x = u and a = u;
```
Here it is possible to sythesize and push down a `x = a` filter, and so the
`JoinOrderBuilder` would do this and add it to the group:
```
group (xy join ab on true), (xy join ab on x = a)
```
Later joins would use this group as an input, an expect the `x = a` filter to
be present. If costing happened to choose the first expression in the group,
we would end up choosing a plan like this:
```
(xy join ab on true) join uv on x = u
```
Where the `a = u` filter isn't included in the top-level join because it
would be redundant to add it when `x = u` and `x = a` are already present.
This is a bit of a simplification, but is essentially the problem fixed
by this commit.

This commit adds a check to the `JoinOrderBuilder` to identify cases where
filters (including ones sythesized from the transitive closure) weren't
pushed all the way down in the original join tree. When this is true, none
of the originally matched joins can be reused when reordered joins are
built except for the root join. This solution may perform some duplicate
work when filters aren't pushed down, but it shouldn't matter because this
case is rare (and should be avoided whenever possible).

Fixes #88659

Release note (bug fix): Fixed a bug introduced in 20.2 that could cause
filters to be dropped from a query plan with many joins in rare cases.