fix(unreal): use FProperty constructors without EObjectFlags on UE 5.8

[kbrizov]

Summary

UE 5.8 deprecates the FField / FProperty constructors that take an EObjectFlags argument. Every property created in ContainerMeta.cpp used that overload, so building the JsEnv module on 5.8 produced 14 C4996 warnings with the note that the parameter must be removed before the next engine release. This PR switches those call sites to the two-argument constructor on 5.8 and later, and leaves earlier engines untouched.

Changes

ContainerMeta.cpp only:

• A file-local macro PUERTS_NEW_PROPERTY(Type, Owner, Name) expands to new Type(Owner, Name) when ENGINE_MAJOR_VERSION > 5 || (ENGINE_MAJOR_VERSION == 5 && ENGINE_MINOR_VERSION >= 8), and to the existing new Type(Owner, Name, RF_Transient) otherwise. It is #undef'd at the end of the file.
• The 14 new F…Property(…, RF_Transient) expressions (bool, byte, int, float, double, int64, string, text, name, object, struct, enum, the enum's underlying byte property, and the byte-enum property) now go through the macro.
• A comment explains why dropping RF_Transient on 5.8 is correct: 5.8 also deprecates FField::FlagsPrivate, which is superseded by FProperty::PropertyFlags, and this file already sets those via CPF_*.

No behaviour change is intended on any engine version.

Verification

Full Development editor builds from a clean Intermediate/ and Binaries/ on Windows, Epic Launcher engines, default V8 9.4.146.24, warning lists compared line by line against the unmodified plugin:

• UE 5.8: build succeeds; the warning list goes from 55 to 41 unique lines. The 14 removed lines are exactly the ContainerMeta.cpp C4996 warnings. No warning was added.
• UE 5.7: build succeeds; the warning list is identical to the unmodified plugin (53 lines).
• Editor sessions on both versions load the plugin and run the declaration generator and a TypeScript Blueprint class through PIE without regression.

Notes for reviewers

• The macro exists only to keep the version check in one place; each call site is otherwise a one-line change.
• The change is independent of the reserved-word declaration fix submitted separately; the two apply cleanly in either order.

[heitara]

LGTM!