[foreign-jextract] RFR: 8252686: All jextract tests should be run in both classes and sources mode

[Athijegannathan Sundararajan]

adding --source mode for all jextract tests

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Commit messages:
 - 8252686: All jextract tests should be run in both classes and sources mode

Changes: https://git.openjdk.java.net/panama-foreign/pull/301/files
 Webrev: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=301&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8252686
  Stats: 135 lines in 13 files changed: 117 ins; 0 del; 18 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/301.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/301/head:pull/301

PR: https://git.openjdk.java.net/panama-foreign/pull/301