internal/core/adt: fix deduping of pattern constraints

Just as with deduping conjuncts from regular
fields, we need to add an ID to the equivlance
set of conjuncts derived from patterns.

This is analogous to https://cuelang.org/cl/1212025

Fixes #3843

Signed-off-by: Marcel van Lohuizen <[email protected]>
Change-Id: Icf051d3ca5874c3c6793c781d1d84907c63871f7
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1212042
TryBot-Result: CUEcueckoo <[email protected]>
Reviewed-by: Matthew Sackman <[email protected]>
Unity-Result: CUE porcuepine <[email protected]>

Author: mpvl