Introduce a MultiChildLogicalNode base type, which accepts 1 to inf children. Move And/Or under this banner.
Xor is awkward enough to remain under doublechild.
This paves the way for T917.
- LogicalNode
- TrueNode
- FalseNode
- SingleChildLogical
- Not
- DoubleChildLogical
- Xor
- MultiChildLogical
- And
- Or