rc: a getter read is settled like a call

[ASDAlexander77]

Under -mm=rc, a value read through a getter was never released. The first leftover from phase 4 (spec §15.3).

Cause

A getter retains its result, as every function does (+1 convention, §9.24). OwnedReturnConsumptionPass settles who owns that reference, but it only looked at ts.CallIndirect. A getter read stays an accessor op (ts.Accessor, ThisAccessor, ThisIndirect*, BoundIndirect*) until the affine lowering turns it into a call. So:

• h.cc.x kept the getter's reference, and nothing gave it back.
• let b = h.cc retained it a second time.

Fix

Accessor reads are classified the way calls are:

• a getter named outright;
• a virtual slot: every method with that member name;
• an interface slot: what the vtable globals put there;
• otherwise, the whole-module (closed-world) answer.

Each classified read is then marked, taken over by its receiver, or released at the end of its block.

A getter read with no live use is skipped. Assigning through an accessor first builds a getter read, then rebuilds the op as a setter and leaves the read for the canonicalizer to delete. A release would keep that read alive, which would add a getter call the program never made.

Measured (AOT, measure.ps1, MB)

program	gc	rc before	rc after	own
own_getter_borrow	6.5	12.6	4.8	4.8
h.cc.x in a loop	6.3	10.9	4.6	4.6

Tests

• New own/rc_getter_temporary.ts, JIT + AOT under rc, gc and none. It covers:

  • class getters returning a field and a fresh object;
  • an override that goes through super;
  • a static getter;
  • an interface accessor;
  • a getter result taken by a let, passed to a call, and assigned through.

  Each read comes after a churn(), so a block freed too early would be reused.

• Windows Release: 3235/3235.

• Linux (WSL): 3222/3222.

• -mm=own corpus: unchanged at 303 compiling files.

Independent of #407. Both edit interfaceCallReturnsOwned, so whichever lands second needs a small rebase.

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