RFR: 8248186: Move CDS C++ vtable code to cppVtables.cpp

[Ioi Lam]

I moved the code that supports C++ vtables in the CDS archive from metaspaceShared.cpp to a new file, cppVtables.cpp.
To keep the refactoring straightforward, the code is moved verbatim, except for:

- Methods are renamed from `MetaspaceShared::xx` to `CppVtables::xx`
- Access to `_mc_region` is changed to the inline function `mc_region()`

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Commit messages:
 - 8248186: Move CDS C++ vtable code to cppVtables.cpp

Changes: https://git.openjdk.java.net/jdk/pull/136/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=136&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8248186
  Stats: 696 lines in 7 files changed: 384 ins; 305 del; 7 mod
  Patch: https://git.openjdk.java.net/jdk/pull/136.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/136/head:pull/136

PR: https://git.openjdk.java.net/jdk/pull/136