TCK: Use region timezone IDs to eliminate timezone deprecation warnings when running with JDK 25

[robertpatrick]

This updates the Tags TCK tests to avoid legacy short timezone IDs as executable timezone inputs.

Changes:

• Replaced EST, PST, and MST inputs passed to JSTL timezone attributes and TimeZone.getTimeZone(...) with region IDs:
  • America/New_York
  • America/Los_Angeles
  • America/Denver
• Replaced parse-date input strings that embedded EST with GMT-05:00, preserving the same offset while avoiding the legacy short ID.
• Updated related explanatory test text and golden files where the output describes the timezone value being exercised.

Verification:

• git diff --check passed.
• Targeted source search found no remaining EST, PST, or MST usage in executable timezone inputs.
• Ran the patched tags-tck tests using WebLogic Server and JDK 25 to verify that all tests are passing and the deprecation warnings about the legacy timezone specifiers are no longer present. Tests run: 535, Failures: 0, Errors: 0, Skipped: 0