Remove InferredJARModelsHandler (#1079)

Now, all logic for parsing loading `astubx` files is consolidated into
the `LibraryModelsHandler.ExternalStubxLibraryModels` class and is
uniform for `astubx` files generated via JarInfer or from source code,
which will ease future bug fixes and changes.

We copied over the logic from `InferredJARModelsHandler` for loading
Android SDK models if present. We also update the logic for
`ExternalStubxLibraryModels.nonNullParameters()` and
`ExternalStubxLibraryModels.nullableReturns()` to pull in all the
relevant info from the parsed `astubx` file.

Fixes #1072

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

@@ -214,7 +214,14 @@ private MethodRef(String enclosingClass, String methodName, String fullMethodSig
       this.fullMethodSig = fullMethodSig;
     }
 
-    private static final Pattern METHOD_SIG_PATTERN = Pattern.compile("^(<.*>)?(\\w+)(\\(.*\\))$");
+    /**
+     * Pattern for parsing method signatures. The signature should be in the format: {@code
+     * <T1,T2,...>methodName(ArgType1,ArgType2,...)}.
+     *
+     * @see #methodRef(String, String)
+     */
+    private static final Pattern METHOD_SIG_PATTERN =
+        Pattern.compile("^(<.*>)?(\\w+|<init>)(\\(.*\\))$");
 
     /**
      * Construct a method reference.

nullaway/src/main/java/com/uber/nullaway/handlers/Handlers.java

@@ -51,9 +51,6 @@ public static Handler buildDefault(Config config) {
       // bytecode annotations
       handlerListBuilder.add(new RestrictiveAnnotationHandler(config));
     }
-    if (config.isJarInferEnabled()) {
-      handlerListBuilder.add(new InferredJARModelsHandler());
-    }
     if (config.handleTestAssertionLibraries()) {
       handlerListBuilder.add(new AssertionHandler(methodNameUtil));
     }