Plugins are stored in the Eclipse installation, not in the workspace folder. Thus, one solution will be to install different Eclipse installations for each task, in this case only the necessary plugins will load (and the rest are not available), on the other hand, you need to support at least three parallel Eclipse installations.
Another solution is to disable the activation of the plug-in at startup: in the Settings / General / Startup and Shutdown section, you can disable individual plugins without loading them. The problem with this approach is that it only helps not to load plugins, but its tabs in menus and toolbars will be loaded.
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