Reland "[class] Ship private methods and accessors"

This is a reland of 77b24c06

Original change's description:
> [class] Ship private methods and accessors
> 
> Turns --harmony-private-methods on by default.
> 
> Intent to ship: https://groups.google.com/a/chromium.org/forum/#!msg/blink-dev/HLpO-HC8aKc/TT32fUNPBAAJ
> ChromeStatus page: https://www.chromestatus.com/feature/5700509656678400
> 
> Bug: v8:8330
> Change-Id: I0d9b21cddd5418be8e7059c24fa05ab98de667b9
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2110890
> Reviewed-by: Shu-yu Guo <syg@chromium.org>
> Commit-Queue: Joyee Cheung <joyee@igalia.com>
> Cr-Commit-Position: refs/heads/master@{#66933}

Bug: v8:8330
Change-Id: I165e54982b642757b2e9ed9eb42a051ea928703b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2130451Reviewed-by: Shu-yu Guo <syg@chromium.org>
Commit-Queue: Joyee Cheung <joyee@igalia.com>
Cr-Commit-Position: refs/heads/master@{#67002}

src/flags/flag-definitions.h

@@ -227,8 +227,7 @@ DEFINE_IMPLICATION(harmony_import_meta, harmony_dynamic_import)
 #endif
 
 // Features that are complete (but still behind --harmony/es-staging flag).
-#define HARMONY_STAGED_BASE(V)                                     \
-  V(harmony_private_methods, "harmony private methods in class literals")
+#define HARMONY_STAGED_BASE(V)
 
 #ifdef V8_INTL_SUPPORT
 #define HARMONY_STAGED(V)                                  \
@@ -243,15 +242,16 @@ DEFINE_IMPLICATION(harmony_import_meta, harmony_dynamic_import)
 #endif
 
 // Features that are shipping (turned on by default, but internal flag remains).
-#define HARMONY_SHIPPING_BASE(V)                               \
-  V(harmony_namespace_exports,                                 \
-    "harmony namespace exports (export * as foo from 'bar')")  \
-  V(harmony_sharedarraybuffer, "harmony sharedarraybuffer")    \
-  V(harmony_import_meta, "harmony import.meta property")       \
-  V(harmony_dynamic_import, "harmony dynamic import")          \
-  V(harmony_promise_all_settled, "harmony Promise.allSettled") \
-  V(harmony_nullish, "harmony nullish operator")               \
-  V(harmony_optional_chaining, "harmony optional chaining syntax")
+#define HARMONY_SHIPPING_BASE(V)                                   \
+  V(harmony_namespace_exports,                                     \
+    "harmony namespace exports (export * as foo from 'bar')")      \
+  V(harmony_sharedarraybuffer, "harmony sharedarraybuffer")        \
+  V(harmony_import_meta, "harmony import.meta property")           \
+  V(harmony_dynamic_import, "harmony dynamic import")              \
+  V(harmony_promise_all_settled, "harmony Promise.allSettled")     \
+  V(harmony_nullish, "harmony nullish operator")                   \
+  V(harmony_optional_chaining, "harmony optional chaining syntax") \
+  V(harmony_private_methods, "harmony private methods in class literals")
 
 #ifdef V8_INTL_SUPPORT
 #define HARMONY_SHIPPING(V)                               \