RFR: 8323999: KeyAgreement cannot be initiated again after a failed initialization

[Matthew Donovan]

This PR updates KeyAgreement to re-initialize the `serviceIterator` field when chooseProvider() is called and serviceIterator.hasNext() returns false. This can happen if KeyAgreement object has been initialized with an invalid key and then initialized with a valid key. (See accompanying test.)

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Commit messages:
 - 8323999: KeyAgreement cannot be initiated again after a failed initialization

Changes: https://git.openjdk.org/jdk/pull/28004/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28004&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8323999
  Stats: 72 lines in 2 files changed: 72 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/28004.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28004/head:pull/28004

PR: https://git.openjdk.org/jdk/pull/28004