RFR: 8216303: JFR: Simplify generated files

[Erik Gahlin]

Hi,

Could I have a review of a fix that removes legacy in the generated JFR event files, in particular hard coded numbers for type / event IDs. Event IDs are now numbered from zero, which has the benefit that most of them can be represented as a single byte instead of two. This will reduce the size of recordings with a few percent.

I’m looping in build-dev, since I am modifying make/src/classes/build/tools/jfr/GenerateJfrFiles.java, but there are no changes to how things are built. The generated JFR files are just slightly different. 

Old and new files:
http://cr.openjdk.java.net/~egahlin/8216303_generated/

Bug:
https://bugs.openjdk.java.net/browse/JDK-8216303

Webrev:
http://cr.openjdk.java.net/~egahlin/8216303/

Testing: 
- Building with and without jfr the feature enabled
- Tier 1/2 (Mac, Linux and Windows)
- JFR tests in test/jdk/jdk/jfr

Thanks
Erik