RFR: 7031: Build a constant pool explorer page [v2]

[Jean-Philippe Bempel]

> Add under Recording a new Page for ConstantPools
> Help to visualize what's inside constant pools part of a JFR recording
> 
> ![JMC_ConstantPoolsPage](https://user-images.githubusercontent.com/4610701/110855759-13569700-82b7-11eb-9981-deb0b8b5e185.png)
> 
> *Draft*
> - Icon is copy/paste from recording. If you have idea about how to replace it...
> - I have limited the tables to the search toolbar, visible by default
> - a hidden count column for constant values helps you find out when you duplicates constant (for OldObjectSample event issue) should not be useful otherwise

Jean-Philippe Bempel has updated the pull request incrementally with one additional commit since the last revision:

  load state for SASH

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

Changes:
  - all: https://git.openjdk.java.net/jmc/pull/228/files
  - new: https://git.openjdk.java.net/jmc/pull/228/files/a3a17f91..7069d49f

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jmc&pr=228&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jmc&pr=228&range=00-01

  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jmc/pull/228.diff
  Fetch: git fetch https://git.openjdk.java.net/jmc pull/228/head:pull/228

PR: https://git.openjdk.java.net/jmc/pull/228