RFR: 8290715: Fix incorrect uses of G1CollectedHeap::heap_region_containing() [v3]

[Thomas Schatzl]

> Hi all,
> 
>   please review this change that fixes some callers of `G1CollectedHeap::heap_region_containing` to a) fail on trying to get the `Heapregion*` on uncommitted regions and b) change some callers to use the correct `heap_region_containing_or_null` method that had been intended there.
> 
> Also remove some now unneccessary asserts as `heap_region_containing` will fail when it previously returned `nullptr`.
> 
> Testing: tier1-5
> 
> Thanks,
>   Thomas

Thomas Schatzl has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 11 commits:

 - Merge branch 'master' into 8290715-heapregion-containing-no-null
 - Some more removal of unnecessary checks
 - Initial changes
 - Fix the places where the wrong heap_region_containing() method has been used
 - kbarrett review
 - Remove some more casts
 - Revert changes to heap_region_containing()
 - Remove cast
 - Remove unnecessary changes
 - some changes
 - ... and 1 more: https://git.openjdk.org/jdk/compare/97fc8deb...5dc2fc08

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Changes: https://git.openjdk.org/jdk/pull/9584/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9584&range=02
  Stats: 23 lines in 5 files changed: 1 ins; 8 del; 14 mod
  Patch: https://git.openjdk.org/jdk/pull/9584.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9584/head:pull/9584

PR: https://git.openjdk.org/jdk/pull/9584