refactor(esql): Improve MvExpand push-down logic in PushDownMvExpandPastProject

- Refactor condition in semantic equality check for MvExpand push-down
- Modify logic to handle alias comparisons more precisely
- Simplify condition for checking input references in project operations
- Improve code readability and reduce complexity of push-down rule

Author: kanoshiou

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/optimizer/rules/logical/PushDownMvExpandPastProject.java

@@ -49,7 +49,7 @@ protected LogicalPlan rule(MvExpand mvExpand) {
                         if (projections.stream()
                             .anyMatch(
                                 ne -> ne.semanticEquals(alias.child())
-                                    || ne != alias && ne instanceof Alias as && as.child().semanticEquals(alias.child())
+                                    || ne instanceof Alias as && as.child().semanticEquals(alias.child()) && as != alias
                             ) == false) {
                             // The alias's original field is not referenced elsewhere, no need to preserve it,
                             mvExpand = PushDownUtils.resolveRenamesFromProject(mvExpand, pj);