RFR: 8274854: Mnemonics for menu containing numeric text not working [v2]

[Michael Strauß]

> This PR fixes an issue with mnemonic parsing by removing the restriction that a mnemonic symbol must be a letter. Now, it can be any character except whitespace.

Michael Strauß has updated the pull request incrementally with one additional commit since the last revision:

  Removed isExtendedMnemonic check from isSimpleMnemonic

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Changes:
  - all: https://git.openjdk.java.net/jfx/pull/647/files
  - new: https://git.openjdk.java.net/jfx/pull/647/files/7cc78d4a..af670b07

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jfx&pr=647&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jfx&pr=647&range=00-01

  Stats: 18 lines in 1 file changed: 5 ins; 9 del; 4 mod
  Patch: https://git.openjdk.java.net/jfx/pull/647.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/647/head:pull/647

PR: https://git.openjdk.java.net/jfx/pull/647