RFR: 8255285: Move JVMFlag origins into a new enum JVMFlagOrigin [v2]

[Ioi Lam]

> Many JVM function take an `JVMFlag::Flags` parameter to indicate the origin of the flag -- i.e., "who is setting this flag". E.g., in arguments.hpp:
> 
> static bool parse_argument(const char* arg, JVMFlag::Flags origin);
> 
> However, `JVMFlag::Flags` contains many other bits that are unrelated to the origin. We should add a new enum `JVMFlagOrigin` that has only the valid values for the origin. This makes it possible to do more type-safety checks at C++ compilation time.
> 
> This patch also renamed the confusing bit `JVMFlag::ORIG_COMMAND_LINE` to `WAS_SET_IN_COMMAND_LINE` and added documentation, so that it won't be confused with `JVMFlagOrigin::COMMAND_LINE`.

Ioi Lam has updated the pull request incrementally with one additional commit since the last revision:

  Removed aliases of JVMFlagOrigin::X as JVMFlag::X

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/823/files
  - new: https://git.openjdk.java.net/jdk/pull/823/files/ab814837..53fed1b0

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=823&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=823&range=00-01

  Stats: 80 lines in 11 files changed: 0 ins; 10 del; 70 mod
  Patch: https://git.openjdk.java.net/jdk/pull/823.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/823/head:pull/823

PR: https://git.openjdk.java.net/jdk/pull/823