RFR (S): 8184347: Move G1CMBitMap and support classes into their own files

[Roman Kennke]

Hi Thomas,

this change looks good to me.

Roman (not an official reviewer)

> Hi all,
>
>   can I have reviews for this wrap-up of the G1CMBitmap cleanup? It
> simply moves all G1CMBitmap related code into their own files.
>
> Although it's a large change, it's really only moving code.
>
> Depends on JDK-8184346, based on webrev.3.
>
> CR:
> https://bugs.openjdk.java.net/browse/JDK-8184347
> Webrev:
> http://cr.openjdk.java.net/~tschatzl/8184347/webrev/
> Testing:
> jprt
>
> Thomas
>