[jmc-graphics] RFR: 7453: Add heat map icon

[Marcus Hirt]

For cimi's heat map view.

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Commit messages:
 - 7453: Add heat map icon

Changes: https://git.openjdk.java.net/jmc-graphics/pull/7/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jmc-graphics&pr=7&range=00
  Issue: https://bugs.openjdk.java.net/browse/JMC-7453
  Stats: 0 lines in 3 files changed: 0 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jmc-graphics/pull/7.diff
  Fetch: git fetch https://git.openjdk.java.net/jmc-graphics pull/7/head:pull/7

PR: https://git.openjdk.java.net/jmc-graphics/pull/7