RFR: 8263002: Remove CDS MiscCode region [v2]

[Ioi Lam]

> The CDS MiscCode region is used for:
> (a) C++ vtables
> (b) Method trampolines
> 
> (a) can be moved to the ReadWrite region
> (b) were introduced in JDK-8145221 so we can delay writing into Methods. This was intended to improve copy-on-write sharing to reduce memory footprint. However, this hasn't been shown to have any significant effect (footprint of metadata usually is much smaller than the Java heap), and introduces a lot of complexity in the HotSpot code.
> 
> Removing (b) will make it easier to implement JDK-8026297 (Generating AdapterHandlerEntry during CDS dump), which will further improve start-up time.
> 
> ============
> Other benefits of removing the MiscCode region:
> 
> - We no longer have a read/write/executable region. This address the concern in JDK-8262922.
> - We can enable CDS on macOS/AArch64, which does not allow read/write/executable regions. (JDK-8253795)

Ioi Lam has updated the pull request incrementally with two additional commits since the last revision:

 - bumped CURRENT_CDS_ARCHIVE_VERSION by one since format has changed
 - @coleenp review: remove temp debug code; fixed accounting of vtable sizes

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/2861/files
  - new: https://git.openjdk.java.net/jdk/pull/2861/files/1c6ac95e..a3e4f25e

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=2861&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=2861&range=00-01

  Stats: 25 lines in 7 files changed: 10 ins; 5 del; 10 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2861.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2861/head:pull/2861

PR: https://git.openjdk.java.net/jdk/pull/2861