A quick rundown of the current state of LW401

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Hi valhalla community,
Since the introduction of the idea of null restriction, the valhalla model
has undergone a huge brainstorm and become much simpler and more
backward-compatible in the new lw401; however, valhalla-docs is now
outdated, especially part 3, the JVM model, and there is no good single
source of truth to look at for our current status.

Here are the most significant changes from the existing documents per my
understanding:
1. Primitive/Inlined classes become special storage of value classes with
default instance and non-atomicity, removing the artificial primitive-value
split and the Q descriptors, leaving just right information for VM to
choose to inline; now we are looking at checked types, but it is still up
to debate (ASM visitor compatibility concerns from Rémi).
2. Value class construction now reuses new-dup-init sequence (shout out to
John Rose for his innovations), with larval-stage and final semantics
guaranteed by writing before super calls.
3. Identity becomes a feature, valueness is determined by ACC_IDENTITY (old
ACC_SUPER), previous ACC_VALUE and ACC_PERMITS_VALUE gone; abstract classes
can become value yet can be extended by identity classes. Uses custom
handling of Object class (construction, superclass rule) to preserve
compatibility and removed marker interfaces
4. Legacy primitives still somewhat differ from the wrappers, such as ==
for double vs Double raw bits, whether Double/Long should tear (currently
they don't, but their primitives do) but this is more of long-term
consideration
5. VM implementation will consider the compatibility with lilliput, as we
seem to require 4 bits in the header. (value, larval, flattened array,
null-free array)

Am I missing anything important here? I wish we can update the notes
somewhere so that we don't have to dig through the mailing list.

Regards,
Chen Liang
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