Code completion proposals for Throwable types should have higher relevance within catch parameter

[eric-milles]

Similar to #419, when completing within a catch parameter list, Throwable types should have boosted relevance.

try {
} catch (Th) { // Throwable should be at the top of the list for Ctrl-Space before ')'
} catch (Exception | Er) { // Error should be at the top of the list for Ctrl-Space before ')'
}

Note: Parser error recovery may be required for catch (Exception | Er) where the parameter name is not yet supplied.

[eric-milles]

Same goes for completion in throws clause.