RFR: 8256156: JFR: Allow 'jfr' tool to show metadata without a recording [v14]

[Yi Yang]

> Hi all,
> 
> May I please have a review for this minor patch?
> 
> It simplifies the use of subcommand `metadata` of jfr tool. Recording 
> file is no longer mandatory, users can directly use `jfr metadata` to 
> output JDK builtin meta information. As JDK-8256156 mentioned, it also 
> supports events and categories filters:
> $ jfr metadata 
> $ jfr metadata recording.jfr # compatible
> $ jfr metadata --events jdk.ThreadStart,jdk.ThreadEnd
> $ jfr metadata --events jdk.ThreadStart,jdk.ThreadEnd recording.jfr
> $ jfr metadata --categories GC,Detailed
> $ jfr metadata --categories GC,Detailed recording.jfr

Yi Yang has refreshed the contents of this pull request, and previous commits have been removed. The incremental views will show differences compared to the previous content of the PR. The pull request contains one new commit since the last revision:

  reimpl test

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/1904/files
  - new: https://git.openjdk.java.net/jdk/pull/1904/files/690f4224..ff13850c

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=1904&range=13
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=1904&range=12-13

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1904.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1904/head:pull/1904

PR: https://git.openjdk.java.net/jdk/pull/1904