RFR: 8281879: Serial: Merge CardGeneration into TenuredGeneration

[Albert Mingkun Yang]

On Tue, 15 Feb 2022 20:21:16 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

> Mostly mechanical changes; `git diff --color-moved=zebra` probably helps to see the actual (small) change, such as dropping the `virtual` modifier, introducing small helper methods to avoid naming collision, etc.
> 
> Test: tier1-6

Thanks for the review.

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PR: https://git.openjdk.java.net/jdk/pull/7482