Improve relevance of magic methods in code completion

[citizenmatt]

Improves the relevance of Unity's magic methods in code completion, pushing them to the top above expected types. Does this by adding the items in "light" completion mode, rather than "full", which gives them a relevance boost. The methods all come from in-memory data structures, so this should be light enough and not affect performance.

Also works around an issue with match highlighting of these methods. See RSRP-466980.

Fixes #260