[flow analysis] Rename SsaNode.getOrCreatePropertyNode.

The old name (`getProperty`) was unclear because (a) the thing being
returned isn't the property itself but the property's SSA node, and
(b) it didn't give any indication that if the property node was not
present, it would be created.

Thanks to Konstantin for pointing this out.

Change-Id: Ib64315b0bb635545c0ee9253c965277c391f36c4
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/418661
Reviewed-by: Konstantin Shcheglov <[email protected]>
Auto-Submit: Paul Berry <[email protected]>
Commit-Queue: Konstantin Shcheglov <[email protected]>

Author: stereotype441

pkg/_fe_analyzer_shared/lib/src/flow_analysis/flow_analysis.dart

@@ -3858,7 +3858,7 @@ class SsaNode<Type extends Object> {
   /// If a new SSA node is created, it is allocated a fresh promotion key using
   /// [promotionKeyStore], so that type promotions for it can be tracked
   /// separately from other type promotions.
-  _PropertySsaNode<Type> getProperty(
+  _PropertySsaNode<Type> getOrCreatePropertyNode(
       String propertyName, PromotionKeyStore<Object> promotionKeyStore,
       {required bool isPromotable}) {
     if (isPromotable) {
@@ -6034,9 +6034,9 @@ class _FlowAnalysisImpl<Node extends Object, Statement extends Node,
     bool isPromotable = propertyMember != null &&
         fieldPromotionEnabled &&
         operations.isPropertyPromotable(propertyMember);
-    _PropertySsaNode<Type> propertySsaNode = targetSsaNode.getProperty(
-        propertyName, promotionKeyStore,
-        isPromotable: isPromotable);
+    _PropertySsaNode<Type> propertySsaNode =
+        targetSsaNode.getOrCreatePropertyNode(propertyName, promotionKeyStore,
+            isPromotable: isPromotable);
     Type? promotedType;
     if (isPromotable) {
       PromotionModel<Type>? promotionInfo =