[lworld] RFR: 8374006: [lworld] Improve field accessor methods in InlineTypeNode

[Marc Chevalier]

This PR remove from `InlineTypeNode` the methods:

int     field_offset(uint index) const;
uint    field_index(int offset) const;
ciType* field_type(uint index) const;
bool    field_is_flat(uint index) const;
bool    field_is_null_free(uint index) const;
bool    field_is_volatile(uint index) const;
int     field_null_marker_offset(uint index) const;

in favor of a single

ciField*      field(uint index) const;

from which we directly access the various properties we are interested in.

I've called it `field` as suggested in the original discussion. I've started with `declared_nonstatic_field_at` to be consistent with `ciInstanceKlass` and to avoid ambiguity wrt which kind of fields we are talking about, but this name is rather long... Since we are only talking about the declared fields, and we have no easy getter for `nonstatic_field_at`, then I think it's ok to have a shorter name. Also, in the context of a `InlineTypeNode`, the "non-static" part of the long name seems rather redundant.

The other question is what we should do with asserts? Methods `field_is_flat`, `field_is_null_free` and `field_is_volatile` had the assert

assert(!field->is_flat() || field->type()->is_inlinetype(), "must be an inline type");

and `field_null_marker_offset` had

assert(field->is_flat(), "must be an inline type");


I've tried to propagate them to the call-site of such functions, and where it makes a bit of sense, and not subsumed by surrounding `if()` and `assert`. Let me know if it seems unnecessary or not well-placed in some cases.

Tested with tier1,tier2,tier3,hs-precheckin-comp,hs-comp-stress,valhalla-comp-stress. Looks fine, but it doesn't seem too risky.

Thanks,
Marc

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

Commit messages:
 - Cleanup
 - InlineTypeNode::field(uint) const

Changes: https://git.openjdk.org/valhalla/pull/1922/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1922&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8374006
  Stats: 134 lines in 4 files changed: 36 ins; 39 del; 59 mod
  Patch: https://git.openjdk.org/valhalla/pull/1922.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1922/head:pull/1922

PR: https://git.openjdk.org/valhalla/pull/1922