implement action idris2.getAvailableModules and idris2.addModuleImport

[srghma]

I am using them like this https://github.com/srghma/nvimmer-ps/blob/master/lua/nvimmer-ps/init.lua#L144C6-L144C32

defined somewhere here https://github.com/search?q=repo%3Anwolverson%2Fpurescript-language-server%20getAvailableModules&type=code

P.S. but in reality - they are not very useful bc if there is undefined name error - then quickaction has import module. This quickaction suggestions are the most important, rn there is no import XXX suggestions, No code actions available