RFR: 8365594: Strengthen Universe klasses asserts to catch bootstrapping errors earlier

[Aleksey Shipilev]

On Fri, 15 Aug 2025 10:43:55 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> I am chasing a Shenandoah + CDS bootstrapping problem, where Shenandoah tries to insert the filler at the time when Universe is not yet initialized. It currently fails rather cryptically on attempt to store `null` class. We could really use an assert on accessing various `Klass` definitions in Universe.
> 
> We already do this for `TypeArrayKlass-es`, so this change would cover `fillerArrayKlass` and `objectArrayKlass`. 
> 
> Additional testing:
>  - [x] Shenandoah + CDS reproducer crashes reliably
>  - [x] Linux AArch64 server fastdebug, `all`

Thanks! Here goes.

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PR Comment: https://git.openjdk.org/jdk/pull/26797#issuecomment-3197475866