Improve the documentation and future-proofing of the GhidraDevPlugin PyDev dependencies (9.3.0 broken/unavailable)

[subreption-research]

Describe the bug Currently the GhidraDevPlugin depends on PyDev, in the past issues like #5980 creeped up as PyDev has moved forward well past 3 major versions (currently 12.x). This dependency on versions that are deprecated can cause issues.

It seems the 9.3.0 repositories are finally broken, including those pointing at HTTP-only mirrors that should not be readily trusted.

To Reproduce Steps to reproduce the behavior:

1. Setup the build environment as documented in Building and Advanced Development
2. Follow the Eclipse-related steps.
3. See error

Expected behavior The current situation should be documented further to include at least a reference to the extant (still working) repositories for the PyDev packages:

https://www.pydev.org/update_sites/ https://www.pydev.org/update_sites/9.3.0/ (all broken)

Environment (please complete the following information):

• OS: Ubuntu 24.04 development environment
• Java Version: 21
• Ghidra Version: current master/git
• Ghidra Origin: Official github repo

Screenshots

[subreption-research]

It seems https://github.com/fabioz/Pydev/releases/download/pydev_9_3_0/ is broken but the release itself is still present at the release page:

https://github.com/fabioz/Pydev/releases/tag/pydev_9_3_0

It might be enough to add the link to the README.