Use accessors for readonly properties

[Dionysusnu]

This resolves the workaround where properties that are read access None but write access PluginSecurity had to be marked writable in None.d.ts to avoid the TS error "All declarations of 'property' must have identical modifiers. (2687)".

We can actually specify these in None.d.ts with a get accessor. When a set accessor is missing, that makes the property readonly. We specify the set accessors in PluginSecurity.d.ts, so that when plugin types are enabled, they make it a regularly accessible property.

[osyrisrblx]

This seems like a good idea for me. Can we keep the readonly for properties which aren't writable in any security level?

[Dionysusnu]

I did consider that, but it seems quite tricky to do with the way the types generation is laid out. It would be a hack, or a lot of work. Is there any benefit to using readonly, apart from less diff in the PR? I tested and it seems to work the same with just the get() accessor.