Make UnifiedGCLogParser public

[obourgain]

Make it possible to extend it in third party packages.

We have an implementation of this, and it currently extends from UnifiedGenerationalParser for no other reason that it is public.

For more information, there is nothing very exciting about our custom implementation, it just collects all the info printed on start:

[2025-11-10T02:00:05.581+0100][0.005s] Parallel Workers: 2
[2025-11-10T02:00:05.581+0100][0.005s] Compressed Oops: Enabled (32-bit)
[2025-11-10T02:00:05.581+0100][0.005s] Version: 21.0.8+9-LTS (release)
[2025-11-10T02:00:05.581+0100][0.005s] Memory: 2048M
[2025-11-10T02:00:05.589+0100][0.012s] Compressed class space mapped at: 0x00007fb2a6000000-0x00007fb2ba000000, reserved size: 335544320
[2025-11-10T02:00:05.581+0100][0.005s] CPUs: 8 total, 1 available
[2025-11-10T02:00:05.580+0100][0.003s] CardTable entry size: 512
...