own: a record literal assigned to a class type is the instance (#492)

[ASDAlexander77]

Under -mm=own, assigning a record literal to a class type was a borrow error ("'this value' borrows a field and cannot be stored, returned or captured"). That covered const p: P = { x: i, items: [i] } and, since #487, the constant { x: 1, items: [1, 2] } too. The literal was built in a temporary slot, and castTupleToClass read each field back out of the slot to store it into a new P. Own treats such a read as a borrow of the slot, and a borrow cannot be stored.

A literal whose receiver is a class (a declaration, a parameter or a result) is now built as the instance itself, by mlirGenObjectLiteralAsClassInstance. Each field's value is stored into the new P as it is: a value made at run time, a number, string or boolean constant, or a constant array copied to a heap array of its own (#479). Own sees fresh values moved into a new object.

This only applies when the literal's fields are exactly the class's. These cases still go through the slot and the cast, unchanged:

• a class with a base;
• a literal missing a field, or holding an extra one;
• any other kind of constant field.

I checked by hand: a base class and a missing required field give the same error as before, and a missing optional field and an extra field work as before. A nested record field still hits own's existing limit on moving an object literal.

The record-variable case of 00record_to_class.ts (let r = {...}; const q: P = r;) moves into a new 00record_variable_to_class.ts. That case shares r's array, which own reports as an error by design. With it moved, 00record_to_class.ts now passes under all four models.

Gate	Result
Windows full suite (Release)	3846/3846
Linux (WSL) full suite	3831/3831
DefaultLib build + its own tests.ps1 -Model, release + debug, compile + JIT	gc 159/159; rc, none 158 passed + weakref_basic skipped (gc only); all "All tests passed"
own corpus, plain and --opt	00record_to_class.ts err → ok; no other flips
rc and own memory, 1M iterations (AOT), the #487 probes	flat at 4.3 MB

Closes #492

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