RFR: 8363928: Specifying AOTCacheOutput with a blank path causes the JVM to crash

[Calvin Cheung]

Added a constraint check for the `AOTCacheOutput` option in order to avoid VM crash in case an empty value is specified.
Update `aotFlags/AOTFlags.java` to test this scenario.

Testing: ran test locally on linux-x64.

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Commit messages:
 - 8363928: Specifying AOTCacheOutput with a blank path causes the JVM to crash

Changes: https://git.openjdk.org/jdk/pull/26518/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=26518&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8363928
  Stats: 11 lines in 4 files changed: 11 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/26518.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26518/head:pull/26518

PR: https://git.openjdk.org/jdk/pull/26518