RFR: 7903830: apidiff: Review glyphs used to indicate same/difference [v2]

[Jonathan Gibbons]

> Please review a medium small fix to change the glyphs used to visually indicate whether elements are the same, different, or in the case of a two-way comparison, added or removed.

Jonathan Gibbons has updated the pull request incrementally with one additional commit since the last revision:

  Add TODO comment in Main

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Changes:
  - all: https://git.openjdk.org/apidiff/pull/17/files
  - new: https://git.openjdk.org/apidiff/pull/17/files/d8fa4a23..5e3bf9e5

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=apidiff&pr=17&range=01
 - incr: https://webrevs.openjdk.org/?repo=apidiff&pr=17&range=00-01

  Stats: 2 lines in 1 file changed: 2 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/apidiff/pull/17.diff
  Fetch: git fetch https://git.openjdk.org/apidiff.git pull/17/head:pull/17

PR: https://git.openjdk.org/apidiff/pull/17