Flip --incompatible_disallow_legacy_py_provider

With this flag enabled by default, the legacy "py" struct provider can no longer be given to Python rules. Use PyInfo instead.

For more information see feature tracking issue #7010 and flag migration tracking issue #7298. See #7741 for cleaning up the flag and legacy code paths.

This flag flip was tested by https://buildkite.com/bazel/bazelisk-plus-incompatible-flags/builds/45 ("The following flags didn't break any passing jobs: ...").

RELNOTES[INC]: (Starlark rules) The legacy "py" provider can no longer be passed to or produced by native Python rules; use [PyInfo](https://docs.bazel.build/versions/master/skylark/lib/PyInfo.html) instead. See [#7298](#7298) for more information.

Fixes #7298, fixes #7010.

PiperOrigin-RevId: 238667805

src/main/java/com/google/devtools/build/lib/rules/python/PythonOptions.java

@@ -216,7 +216,7 @@ public String getTypeDescription() {
 
   @Option(
       name = "incompatible_disallow_legacy_py_provider",
-      defaultValue = "false",
+      defaultValue = "true",
       documentationCategory = OptionDocumentationCategory.STARLARK_SEMANTICS,
       effectTags = {OptionEffectTag.LOADING_AND_ANALYSIS},
       metadataTags = {