Changing grammar for decorators that don't have parenthesis

This reverts commit dee508b.

Test fixtures (e.g. `ProxyDeserialization.class` at the default package)
were previously compiled into `${compile.dir}` and bundled into
`${jython.dev.jar}`, breaking downstream OSGi bundle wrapping in
consumers that pull `jython3` as a transitive Maven dependency.
See wala/ML#557.

Co-Authored-By: Claude Opus 4.7 (1M context) <[email protected]>

Compile `tests/java` to a separate `test-classes` directory

The grammar parsed an annotated assignment `name: type [= value]` as either a
plain `Assign` (dropping the annotation) or, for the annotation-only form, as a
bare `Expr` holding just the annotation expression with the target name thrown
away. There was no `AnnAssign` AST node at all (only function-argument
annotations, PEP-3107, were modeled).

Add the `AnnAssign(expr target, expr annotation, expr? value, int simple)` node
to the ASDL and the generated AST (via `asdl_antlr.py`), register it in the
visitor interface/base and `AstModule`, and rewrite the `expr_stmt` annotation
branch to build an `AnnAssign` that retains the target, annotation, and optional
value. This lets downstream consumers recover annotated class fields (notably
`NamedTuple`/dataclass declarations) and their declaration order.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

Address review on the PEP-526 `expr_stmt` branch:
- Compute `simple` from the target (1 for a bare `Name`, else 0) instead of
  hard-coding 1.
- Restore `yield_expr` on the right-hand side (`x: int = yield y`), which the
  prior assignment branch accepted and the first cut dropped.
- Validate the target via a new `GrammarActions.checkAnnAssign`: a single
  `Name`/`Attribute`/`Subscript` may be annotated; tuple, list, and starred
  targets are rejected, matching CPython.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

`py2int` returned null for anything but a Java `Integer`, so constructing an AST
node from Python with an integer field (`AnnAssign.simple`, `ImportFrom.level`,
`FormattedValue.conversion`) silently stored null and threw a
`NullPointerException` on read via unboxing. Accept a `PyObject` integer (via
`asInt()`); `None` and other non-integer objects still map to null.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

Two review follow-ups:
- The annotation expression was parsed with a null context, so its `Name` nodes
  had no `ctx`. Now that the annotation is preserved (rather than dropped),
  parse it in `Load` context so annotation names read as references rather than
  being treated as bound.
- `checkAnnAssign` reported "not tuple" for an AST `List` target; give a distinct
  "not list" message, matching CPython.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

The asInt-based version threw `TypeError` for non-integer objects rather than
mapping them to null, so the comment was inaccurate. Convert only `PyInteger`/
`PyLong` (the Python int types) and map everything else — including `None` and
non-integer objects — to null, matching the prior lenient contract.

Now that the parser emits `AnnAssign`, the bytecode compiler needs a
`visitAnnAssign`: without it the node fell through to `VisitorBase`'s
unhandled-and-traverse default, which walks the `Store` target and emits
incorrect bytecode, and `x: T = v` no longer performed its assignment.

Emit the assignment when a value is present (evaluate the value, store to the
target, mirroring `visitAssign`); an annotation-only `x: T` binds nothing. The
annotation is not evaluated and `__annotations__` is not updated, consistent
with this compiler's existing limited annotation support. `ScopesCompiler`/
`ArgListCompiler` need no change: they don't override `visitAssign` and record
bindings via `visitName` during the default traversal, which handles `AnnAssign`
the same way (the annotation parses in Load context, so it isn't mis-bound).

Co-Authored-By: Claude Opus 4.8 <[email protected]>

Previously `checkAnnAssign` only flagged tuple, list, and starred targets.
`checkGenericAssign` covers numbers, strings, calls, operators, and
comprehensions, but not dict/set literals or `True`/`False`, so those built an
`AnnAssign` with a non-storeable target that broke later at
`CodeCompiler.visitAnnAssign`'s `set(target)`. Replace the trailing
target-specific checks with a positive allow-list of `Name`/`Attribute`/`Subscript`,
matching CPython's "illegal target for annotation".

Co-Authored-By: Claude Opus 4.8 <[email protected]>

Support PEP-526 variable annotations (`AnnAssign`)