Update ruby and mmtk-core repo rev

This is a reguler merging commit that synchronizes the MMTK's CRuby fork
with the upstream.

The upstream introduced the imemo:fields type, and is now using it for
the `generic_fields_tbl_`, i.e. it now holds instance variables for
objects other than `T_OBJECT`, `T_CLASS` and `T_MODULE`.  When using
MMTk, we treat the key-value pair in the `generic_fields_tbl_` as a
strong edge, i.e. treating the imemo:fields of an object as if it were a
child.  We now update the `generic_fields_tbl_` like other weak tables.
This simplified the handling of generic fields table in the MMTk
binding.

With imemo:fields added, we now have 17 imemo types including MMTk's
imemo:mmtk_strbuf and imemo:mmtk_objbuf.  We increased the header bits
of the imemo type to 5 bits and changed the value of some imemo-specific
header offsets, such as `ISEQ_TRANSLATED`.

The upstream changed the API for acquiring/releasing the GVL.  We make
changes accordingly.

YJIT assumes there is only one thread doing GC.  It panics when two GC
worker threads try to mark two iseq objects simultaneously.  We made
several changes to support parallel GC for YJIT-compiled iseq objects:

1.  We replaced `Block::gc_obj_offsets` with `Block::gc_obj_addresses`
    which are now absolute pointers instead of offsets.  By doing so, we
    no longer need to borrow the `Rc<RefCell<VirtualMem>>` during GC.
2.  `rb_yjit_iseq_update_references` no longer uses `CodeBlock` to write
    code, and no longer calls `mark_all_executable` after updating each
    object.  Instead we make the whole code memory writable before
    updating any objects, and make it executable after the updating
    phase finishes.  This should both make it friendly to parallel GC
    and improve performance.

Author: wks

mmtk/Cargo.lock

@@ -12,7 +12,7 @@ edition = "2021"
 # Metadata for the Ruby repository
 [package.metadata.ci-repos.ruby]
 repo = "mmtk/ruby" # This is used by actions/checkout, so the format is "owner/repo", not URL.
-rev = "820a028762342fb44b34954a49fa2faec8563198"
+rev = "38be667194be94e8e9adf9b248a19e54f4e198b7"
 
 [lib]
 name = "mmtk_ruby"
@@ -37,7 +37,7 @@ features = ["is_mmtk_object", "object_pinning", "sticky_immix_non_moving_nursery
 
 # Uncomment the following lines to use mmtk-core from the official repository.
 git = "https://github.com/mmtk/mmtk-core.git"
-rev = "3d89bb51c191d3077278684ec5059726128d3e2b"
+rev = "8dcfcc32c30eaf0f2a8d7f93489e465f215af093"
 
 # Uncomment the following line to use mmtk-core from a local repository.
 #path = "../../mmtk-core"