RFR: 8253402: Convert vmSymbols::SID to enum class [v2]

[Ioi Lam]

> Convert `vmSymbols::SID` to an `enum class` to provide better type safety.
> 
> - The original enum type `vmSymbols::SID` cannot be forward-declared. I moved it out of the `vmSymbols` class and
>   renamed, so now it can be forward-declared as `enum class vmSymbolID : int;`, without including the large vmSymbols.hpp
>   file.
>   - This also breaks  the mutual dependency between the `vmSymbols` and `vmIntrinsics` classes. Now  the declaration of
>     `vmIntrinsics` can be moved from vmSymbols.hpp to vmIntrinsics.hpp, where it naturally belongs.
> - Type-safe enumeration (contributed by Kim Barrett)
> for (vmSymbolID index : vmSymbolsIterator()) {
>    vm_symbol_index[as_int(index)] = index;
> }
> - I moved `vmSymbols::_symbols[]` to `Symbol::_vm_symbols[]`, and made it accessible via `Symbol::vm_symbol_at()`. This
>   way, header files (e.g. fieldInfo.hpp) that need to convert from `vmSymbolID` to `Symbol*` don't need to include the
>   large vmSymbols.hpp file.
> - I changed the `VM_SYMBOL_ENUM_NAME` macro so that the users don't need to explicitly add the `vmSymbolID::` scope.
> - I removed many unnecessary casts between `int` and `vmSymbolID`.
> - The remaining casts are done via `vmSymbol::as_int()` and `vmSymbols::as_SID()` with range checks.
> 
> -----
> If this is successful, I will do the same for `vmIntrinsics::ID`.

Ioi Lam has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes
the unrelated changes brought in by the merge/rebase. The pull request contains six additional commits since the last
revision:

 - more vmEnums.hpp fixes; fixed minimal VM build
 - Merge branch 'master' into 8253402-convert-vmsymbols-sid-to-enum-class
 - Moved forward declaration of vmSymbolID to vmEnums.hpp
 - clean up whitespaces and removed useless comment
 - removed unnecessary include
 - 8253402: Convert vmSymbols::SID to enum class

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/276/files
  - new: https://git.openjdk.java.net/jdk/pull/276/files/443cf52a..1ad27fdb

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=276&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=276&range=00-01

  Stats: 30598 lines in 679 files changed: 5310 ins; 23542 del; 1746 mod
  Patch: https://git.openjdk.java.net/jdk/pull/276.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/276/head:pull/276

PR: https://git.openjdk.java.net/jdk/pull/276