RFR: 8294076: Improve ant detection in idea.sh

[Magnus Ihse Bursie]

The ant detection in bin/idea.sh is very rudimentary. It fails at a modern aarch64 macOS installation.

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Commit messages:
 - 8294076: Improve ant detection in idea.sh

Changes: https://git.openjdk.org/jdk/pull/10364/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10364&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8294076
  Stats: 23 lines in 1 file changed: 14 ins; 0 del; 9 mod
  Patch: https://git.openjdk.org/jdk/pull/10364.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10364/head:pull/10364

PR: https://git.openjdk.org/jdk/pull/10364