feat(pg): add partial index detection to introspection (#535)

Author: hansololai

packages/graphile-build-pg/src/plugins/PgIntrospectionPlugin.d.ts

@@ -152,6 +152,7 @@ export interface PgIndex {
   indexType: string;
   isUnique: boolean;
   isPrimary: boolean;
+  isPartial: boolean;
   attributeNums: Array<number>;
   attributePropertiesAsc: Array<boolean> | void;
   attributePropertiesNullsFirst: Array<boolean> | void;

packages/graphile-build-pg/src/plugins/PgIntrospectionPlugin.js

@@ -182,6 +182,7 @@ export type PgIndex = {
   isReplicaIdentity: boolean,
   isValid: boolean,
   */
+  isPartial: boolean,
   attributeNums: Array<number>,
   attributePropertiesAsc: ?Array<boolean>,
   attributePropertiesNullsFirst: ?Array<boolean>,

packages/graphile-build-pg/src/plugins/introspectionQuery.js

@@ -375,6 +375,7 @@ with
       idx.indimmediate as "isImmediate", -- enforce uniqueness immediately on insert
       idx.indisreplident as "isReplicaIdentity",
       idx.indisvalid as "isValid", -- if false, don't use for queries
+      idx.indpred is not null as "isPartial", -- if true, index is not on on rows.
       idx.indkey as "attributeNums",
       am.amname as "indexType",
       ${