Fix EditorGetRect opcode

[inikulin]

Plugin should return 1 if it has editor on EditorGetRect opcode, otherwise provided dimensions won't be applied by host.

[inikulin]

Seems like the recent version of clippy is unhappy with the lib code 😕

[crsaracco]

Can confirm this is at least what Carla does: https://github.com/falkTX/Carla/blob/80cf43bec585bfe5e628b4587eac320beeb976c5/source/plugin/carla-vst.cpp#L415

I'll take a look at the clippy errors.

[crsaracco]

Added some more clippy ignores:

• clippy::needless-doctest-main is a false positive in our case, since we need it for the doctests to compile, so that will probably be a permanent ignore.
• clippy::comparison-chain is a style choice that I don't feel is necessary to enforce here, so that will probably be a permanent ignore.
• clippy::missing-safety-doc is something we should fix eventually, so this will be a temporary ignore. I'll make an issue for it in the vst-rs repo after this PR is merged.

[crsaracco]

LGTM.