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

[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

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Commit messages:
 - More removals
 - Easy removals

Changes: https://git.openjdk.org/valhalla/pull/946/files
 Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=946&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8319528
  Stats: 227 lines in 46 files changed: 24 ins; 91 del; 112 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