Type based autocompletion

[zth]

Rough outline of what work to do in what order:

• Type based completion for function arguments Completion snippet support #668
• Complete booleans, options, variant constructors Completion snippet support #668
• Type based completion for JSX props complete JSX prop values #667
• Support snippets in completion items Completion snippet support #668
• Complete polyvariants Complete polyvariants #669
• Complete record construction Nested expression completion #682
• Complete tuples Completion snippet support #668
• Complete nested expressions when constructing values Nested expression completion #682
• Complete patterns in switches Initial pattern completion #670
• Complete patterns when destructing Initial pattern completion #670
• Expand completion option items when appropriate. Some(_) -> Some(true) and Some(false) for example expand options in typed expr/pattern completion #690
• Piggy back on Ppat_any (_) to trigger completion Let ppat_any trigger completion in patterns #692
• Support inline records in completion support completing in/through inline records in variant payloads #695
• Handle optional record fields Handle optional fields in completion #691
• Complete functions (insert empty function) complete function snippets #701
• Complete lowercase jsx props too typed expression completion for lowercase JSX tags #702
• Complete using type annotations [WIP] Annotated completions #711
• "Seen idents" for more patterns
• Leverage "filterText" to ensure module names aren't included when filtering completion list (unless only searching for modules)
• Do not add "any" when inserting variant payloads in expressions

Things to figure out

• Qualify JSX V3 constructors Not doing this, let people upgrade to jsx v4 to fix it
• Fix insertText not being used unless there's snippet support
• Figure out more instances where we want to do typed expr or pattern completion

Future

• Figure out when to expand options in JSX props (read more in description of complete JSX prop values #667). Will need to parse the React component make function and look whether prop is optional or not.