[jdk11u-dev] RFR: 8303809: Dispose context in SPNEGO NegotiatorImpl

[Alexey Bakhtin]

Clean backport from OpenJDK17

sun/security/jgss sun/security/krb5 sun/net/www/protocol/http tests passed successfully

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Commit messages:
 - Backport 10f16746254ce62031f40ffb0f49f22e81cbe631

Changes: https://git.openjdk.org/jdk11u-dev/pull/1906/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=1906&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8303809
  Stats: 70 lines in 5 files changed: 70 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/1906.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev.git pull/1906/head:pull/1906

PR: https://git.openjdk.org/jdk11u-dev/pull/1906