RFR: 8255285: Move JVMFlag origins into a new enum JVMFlagOrigin

[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`.

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Commit messages:
 - fixed whitespaces
 - jvmflagorigin

Changes: https://git.openjdk.java.net/jdk/pull/823/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=823&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8255285
  Stats: 173 lines in 19 files changed: 49 ins; 14 del; 110 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