RFR: 8292606: G1 and Epsilon header cleanup for JDK-8282729

[Axel Boldt-Christmas]

In [JDK-8282729](https://bugs.openjdk.org/browse/JDK-8282729) a few headers where found which were indirectly included via `#include "gc/shared/blockOffsetTable.hpp", [JDK-8282729](https://bugs.openjdk.org/browse/JDK-8282729) moves the Serial part of `blockOffsetTable` into `gc/serial` so those headers needs to be fixed for G1 and Epsilon. These header fixes were moved out of the issue to make the review processes easier. Here is a list of the files in question.
* `src/hotspot/share/gc/epsilon/epsilonHeap.hpp`
    * Uses `VirtualSpace`
* `src/hotspot/share/gc/g1/g1CollectionSetChooser.hpp`
    * Uses `G1MixedGCLiveThresholdPercent`
* `src/hotspot/share/gc/g1/g1FullGCScope.cpp`
    * Uses `MarkSweepDeadRatio`
* `src/hotspot/share/gc/g1/g1HeapRegionEventSender.cpp`
    * Uses `UseG1GC`
* `src/hotspot/share/gc/g1/g1HeapSizingPolicy.cpp`
    * Uses `GCTimeRatio`, `G1ExpandByPercentOfAvailable`, `MaxHeapSize`, `MinHeapSize`, `MaxHeapFreeRatio`, `MinHeapFreeRatio`
* `src/hotspot/share/gc/g1/g1MemoryPool.cpp`
    * Uses `UseG1GC`
* `src/hotspot/share/gc/g1/g1NUMA.cpp`
    * Uses `AlwaysPreTouch`
* `src/hotspot/share/gc/g1/g1RegionToSpaceMapper.cpp`
    * Uses `AlwaysPreTouch`
* `src/hotspot/share/gc/g1/g1SegmentedArrayFreeMemoryTask.cpp`
    * Uses `G1RemSetFreeMemoryStepDurationMillis`

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Commit messages:
 - Cleanup headers

Changes: https://git.openjdk.org/jdk/pull/9921/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9921&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8292606
  Stats: 16 lines in 9 files changed: 10 ins; 1 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/9921.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9921/head:pull/9921

PR: https://git.openjdk.org/jdk/pull/9921