chore(tree): Rename to getAllowedContentIncompatibilities to getAllowedContentDiscrepancies (#23087)

## Description

Updates several functions and types in `discrepancies.ts` to use the
term `Discrepancy` over `Incompatibility`. The general trend I have in
mind which is staged for this code is to move policy decisions about
schema *compatibility* to the simple-tree layer, whereas this function
is a helper that enumerates ways in which two stored schemas are
different. The updated naming should help reflect this.

---------

Co-authored-by: Abram Sanderson <[email protected]>

Author: Abe27342

packages/dds/tree/src/feature-libraries/index.ts

@@ -74,7 +74,7 @@ export {
 	type FieldChangeEncodingContext,
 	type FieldKindConfiguration,
 	type FieldKindConfigurationEntry,
-	getAllowedContentIncompatibilities,
+	getAllowedContentDiscrepancies,
 	isRepoSuperset,
 	isNeverTree,
 } from "./modular-schema/index.js";