gh-115859: Re-enable T2 optimizer pass by default (#116062)

This undoes the *temporary* default disabling of the T2 optimizer pass in gh-115860.

- Add a new test that reproduces Brandt's example from gh-115859; it indeed crashes before gh-116028 with PYTHONUOPSOPTIMIZE=1
- Re-enable the optimizer pass in T2, stop checking PYTHONUOPSOPTIMIZE
- Rename the env var to disable T2 entirely to PYTHON_UOPS_OPTIMIZE (must be explicitly set to 0 to disable)
- Fix skipIf conditions on tests in test_opt.py accordingly
- Export sym_is_bottom() (for debugging)
- Fix various things in the `_BINARY_OP_` specializations in the abstract interpreter:
  - DECREF(temp)
  - out-of-space check after sym_new_const()
  - add sym_matches_type() checks, so even if we somehow reach a binary op with symbolic constants of the wrong type on the stack we won't trigger the type assert

Python/optimizer_analysis.c

@@ -297,6 +297,7 @@ remove_globals(_PyInterpreterFrame *frame, _PyUOpInstruction *buffer,
 #define sym_set_non_null _Py_uop_sym_set_non_null
 #define sym_set_type _Py_uop_sym_set_type
 #define sym_set_const _Py_uop_sym_set_const
+#define sym_is_bottom _Py_uop_sym_is_bottom
 #define frame_new _Py_uop_frame_new
 #define frame_pop _Py_uop_frame_pop
 
@@ -510,12 +511,9 @@ _Py_uop_analyze_and_optimize(
 
     peephole_opt(frame, buffer, buffer_size);
 
-    char *uop_optimize = Py_GETENV("PYTHONUOPSOPTIMIZE");
-    if (uop_optimize != NULL && *uop_optimize > '0') {
-        err = optimize_uops(
-            (PyCodeObject *)frame->f_executable, buffer,
-            buffer_size, curr_stacklen, dependencies);
-    }
+    err = optimize_uops(
+        (PyCodeObject *)frame->f_executable, buffer,
+        buffer_size, curr_stacklen, dependencies);
 
     if (err == 0) {
         goto not_ready;