completions for predicate keywords in Spring Data repositories

[danthe1st]

This PR adds completions for predicate keywords in Spring Data repositories.

For example, it would suggest a completion findByFirstNameAnd when typing findByFirstName.

This is a follow-up to #981.

With this PR, it should now be possible to create most Spring JPA repository methods just with Content assist proposals (and adjusting the return type if wanted).

[danthe1st]

I am unsure whether to actually use CompletionItemKind.Text for those completions. Would other options like Keyword (and maybe Property for property completions) be more appropriate?

[BoykoAlex]

@danthe1st property completion kind for property is more appropriate. As for the query (method name) maybe text is fine... The completion kind only affects the icon description that is supposed to tell you what about to follow once completion item is applied. Since the result is just text the text completion kind seems ok to me.

[danthe1st]

@BoykoAlex
So should I change the property completions in query methods (e.g. findByFirst -> findByFirstName) to use CompletionItemKind.Property?

[BoykoAlex]

Merged with 2e79692

(@danthe1st hmm... the result of the completion is just text, correct? I think in this case it should just remain text)