RFR: 8082: Add ctrl+a keyboard shortcut to select all lanes on jfr threads page

[Alex Macdonald]

This PR addresses JMC-8082 [[0]](https://bugs.openjdk.org/browse/JMC-8082), in which it'd be nice to easily select all the threads on the jfr threads page using a keyboard shortcut. Inspired by https://github.com/openjdk/jmc/pull/492, it would be nice to add more "table" behaviour to the jfr threads page text canvas. In this case, the keyboard shortcut ctrl+a will highlight all of the thread lanes and update the current selection.

[0] https://bugs.openjdk.org/browse/JMC-8082

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Commit messages:
 - 8082: Add ctrl+a keyboard shortcut to select all lanes on jfr threads page

Changes: https://git.openjdk.org/jmc/pull/493/files
 Webrev: https://webrevs.openjdk.org/?repo=jmc&pr=493&range=00
  Issue: https://bugs.openjdk.org/browse/JMC-8082
  Stats: 49 lines in 3 files changed: 44 ins; 2 del; 3 mod
  Patch: https://git.openjdk.org/jmc/pull/493.diff
  Fetch: git fetch https://git.openjdk.org/jmc.git pull/493/head:pull/493

PR: https://git.openjdk.org/jmc/pull/493