When estimating an OR clause using multiple extended statistics
objects, treat the estimates for each set of clauses for each
statistics object as independent of one another. The overlap estimates
produced for each statistics object do not apply to clauses covered by
other statistics objects.

Dean Rasheed, reviewed by Tomas Vondra.

Discussion: https://postgr.es/m/CAEZATCW=J65GUFm50RcPv-iASnS2mTXQbr=CfBvWRVhFLJ_fWA@mail.gmail.com