groupArray returns cannot be nullable

[lgbo-ustc]

Changelog category (leave one):

• Bug Fix

Changelog entry (a user-readable short description of the changes that goes to CHANGELOG.md):

Fixed Nested type Array(T) cannot be inside Nullable type for groupArray function.

closed #48462

[lgbo-ustc]

change the result of groupArray(NULL) from null to []

SELECT groupArray(NULL)

┌─groupArray(NULL)─┐
│ []               │
└──────────────────┘

SELECT toTypeName(groupArray(NULL))

┌─toTypeName(groupArray(NULL))─┐
│ Array(Nullable(Nothing))     │
└──────────────────────────────┘

[nickitat]

let's pray we didn't break backward compatibility

[azat]

This does break the binary format (updated test references shows that there are problems), so I'm suggesting to revert it for now - #49971 (yes one release already affected, but I don't see a way to fix this in a binary compatible way now, and I hope that not a lot people affected by this), and fix it without breaking compatibility (also I found more changes of the on disk format for aggregate functions over Nullable, that comes from #11593)

Thoughts?