Invoke generic method inference in more places (#1286)

Fixes #1262, fixes #1263 

We now invoke inference for generic method calls in more places,
including when it gets queried from dataflow analysis of a full method.
Where possible, we provide a `TreePath` to the relevant call. With this
`TreePath`, we can reconstruct the assignment context of the call and
use that information when performing inference (see the new
`getInvocationAndContextForInference` method). In some cases, we pass
`null` as the `TreePath` since one is not readily available. I _believe_
that in most / all of these cases, inference should have already been
performed for the call, so we should be able to use the cached result.
If / when we find cases where that didn't happen, and it is impacting
the inference result negatively, we can fix in follow ups.

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **New Features**
* Path-aware nullness inference for generic method calls that selects
the correct invocation/assignment context, including nested calls and
assignment sites.
* **Bug Fixes**
* More accurate generic return nullness determination to reduce
incorrect diagnostics in complex call and assignment patterns.
* **Performance**
* Per-invocation caching to speed repeated inference and reuse results
across related calls.
* **Tests**
* Re-enabled and expanded generics inference tests, adding
dataflow-triggered inference scenarios and related assertions.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Author: msridhar

nullaway/src/main/java/com/uber/nullaway/NullAway.java

@@ -2711,9 +2711,12 @@ private boolean mayBeNullMethodCall(
     if (Nullness.hasNullableAnnotation(exprSymbol, config)) {
       return true;
     }
+    // NOTE: we cannot rely on state.getPath() here to get a TreePath to the invocation, since
+    // sometimes the invocation is a sub-node of the leaf of the path.  So, here if inference runs,
+    // it will do so without an assignment context.  If this becomes a problem, we can revisit
     if (config.isJSpecifyMode()
         && genericsChecks
-            .getGenericReturnNullnessAtInvocation(exprSymbol, invocationTree, state)
+            .getGenericReturnNullnessAtInvocation(exprSymbol, invocationTree, null, state)
             .equals(Nullness.NULLABLE)) {
       return true;
     }

nullaway/src/main/java/com/uber/nullaway/dataflow/AccessPathNullnessPropagation.java

@@ -1155,7 +1155,7 @@ private boolean genericReturnIsNullable(MethodInvocationNode node) {
       if (tree != null) {
         Nullness nullness =
             genericsChecks.getGenericReturnNullnessAtInvocation(
-                ASTHelpers.getSymbol(tree), tree, state);
+                ASTHelpers.getSymbol(tree), tree, node.getTreePath(), state);
         return nullness.equals(NULLABLE);
       }
     }