RFR: 8299047: On Ubuntu 22.04 text cursor in TextArea stops blinking after couple of cycles

[Tejesh R]

The issue happens only in xrender and not only specific to cursor blink. On analysis the issue found to common to JTextField and not only to cursor blink. The issue seems to be w.r.t Synchronization of toolkit's graphics state, where buffering of graphics events occurred a delayed painting (As explained in bug [JDK-8068529](https://bugs.openjdk.org/browse/JDK-8068529). This occured only when `xrender` graphics rendering is used (linux). Toolkit synchronization at `BasicTextUI` `paintsafely()` helped solve the issue (As suggested in the referred bug) without causing any regressions.
CI testing results were fine.

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Commit messages:
 - Remove spaces
 - Fix + Manual test

Changes: https://git.openjdk.org/jdk/pull/12939/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12939&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8299047
  Stats: 121 lines in 2 files changed: 121 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/12939.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12939/head:pull/12939

PR: https://git.openjdk.org/jdk/pull/12939