[lworld] RFR: 8319528: [lworld] Remove T_PRIMITIVE_OBJECT from JIT code [v2]

[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 incrementally with one additional commit since the last revision:

  Restored handling in c_calling_convention

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

Changes:
  - all: https://git.openjdk.org/valhalla/pull/946/files
  - new: https://git.openjdk.org/valhalla/pull/946/files/dff12a99..59b0f5fc

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=valhalla&pr=946&range=01
 - incr: https://webrevs.openjdk.org/?repo=valhalla&pr=946&range=00-01

  Stats: 2 lines in 2 files changed: 2 ins; 0 del; 0 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