Three fixes that work together to correct ARC refcount accounting:
1. _ClassFree now delegates to _ClassRelease instead of bypassing ARC
with a raw _BlaiseFreeMem. This lets users call .Free (out of habit)
or rely on ARC — both paths go through the same refcount logic.
2. ExprOwnsRef helper in codegen suppresses the call-site _ClassAddRef
when the RHS expression already owns a +1 reference (function/method
return values). Covers TFuncCallExpr (with ResolvedDecl guard to
exclude type casts), TMethodCallExpr, TFieldAccessExpr.IsMethodCall,
and TIdentExpr.IsNoArgFuncCall / IsImplicitSelfMethod.
3. Allow Pointer() and PtrUInt() casts on tyString arguments, needed by
rtl.platform.posix for Pointer(APath) where APath is a string.
The double-AddRef bug inflated refcounts on every class-returning
function call: the callee's Result := X emitted AddRef (correct — the
Result slot is not released at scope exit), and the caller's assignment
emitted a second AddRef (incorrect — the +1 already transferred).
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