[lworld] RFR: 8319528: [lworld] Remove T_PRIMITIVE_OBJECT from JIT code [v3]

[Tobias Hartmann]

> The JIT code does not need `T_PRIMITIVE_OBJECT` anymore because there are now other ways to determine if a type is null-free / flattenable. I replaced all usages in C1 and C2.
> 
> I also changed the calling convention code to now use `T_METADATA` / `T_VOID` delimiters for scalarized arguments instead of `T_PRIMITIVE_OBJECT` / `T_VOID`. We still need to handle `T_PRIMITIVE_OBJECT` in the signature though until Q-types go away but most of the remaining usages are trivial to remove.
> 
> Best regards,
> Tobias

Tobias Hartmann has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains four additional commits since the last revision:

 - Merge branch 'lworld' into basic_type_cleanup
 - Restored handling in c_calling_convention
 - More removals
 - Easy removals

-------------

Changes:
  - all: https://git.openjdk.org/valhalla/pull/946/files
  - new: https://git.openjdk.org/valhalla/pull/946/files/59b0f5fc..fd69da11

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=valhalla&pr=946&range=02
 - incr: https://webrevs.openjdk.org/?repo=valhalla&pr=946&range=01-02

  Stats: 29 lines in 3 files changed: 8 ins; 10 del; 11 mod
  Patch: https://git.openjdk.org/valhalla/pull/946.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/946/head:pull/946

PR: https://git.openjdk.org/valhalla/pull/946