Move bundles to Java 21

[akurtakov]

They already transitively require it (due to
eclipse-platform/eclipse.platform.swt#2824 ) so this change makes it to state it directly and silence the PDE warnings.

[laeubi]

@akurtakov but then please also raise the lower bound to the once from the dependencies, otherwise you silence the warnings but it makes no sense as then the resolver could still resolve the old bundles.

Otherwise this statement

They already transitively require it (due to eclipse-platform/eclipse.platform.swt#2824 )

is not true... because they only require it transitively if resolved against never SWT versions but not in general!

[github-actions]

Test Results

 3 018 files  ±0   3 018 suites  ±0   2h 14m 42s ⏱️ + 2m 2s
 8 242 tests ±0   7 994 ✅ +1  248 💤 ±0  0 ❌  - 1 
23 646 runs  ±0  22 855 ✅ +1  791 💤 ±0  0 ❌  - 1 

Results for commit aa4e9f7. ± Comparison against base commit 26ddd0d.

[akurtakov]

New warnings are URL constructors being deprecated but these need extra care so not doing it now.