feat: show only missing variant suggestion for enums in patterns completion and bump them in list too
Fixes#12438
### Points to help in review:
- This PR can be reviewed commit wise, first commit is about bumping enum variant completions up in the list of completions and second commit is about only showing enum variants which are not complete
- I am calculating missing variants in analysis.rs by firstly locating the enum and then comparing each of it's variant's name and checking if arm string already contains that name, this is kinda hacky but I didn't want to implement complete missing_arms assist here as that would have been too bulky to run on each completion cycle ( if we can improve this somehow would appreciate some inputs on it )
### Output:
https://user-images.githubusercontent.com/49019259/208245540-57d7321b-b275-477e-bef0-b3a1ff8b7040.mov
Relevant Zulip Discussion: https://rust-lang.zulipchat.com/#narrow/stream/185405-t-compiler.2Frust-analyzer/topic/Issue.20.2312438
