JsLIGO improvements

Type system

• remove need of writing as foo notations (@alistair.obrien + @SanderSpies for syntax)
• add support for iterating over maps (@lesenechal.remi, !1949 (merged))
• remove need for adding annotations for recursive functions (@alistair.obrien, !1960 (merged))
• allow for global mutable variables (@alistair.obrien)
• simplify let z : list <int> = list([2, ...y]); into let z : list <int> = [2, ...y];

Syntax

• Add support for match expression (see: https://github.com/tc39/proposal-pattern-matching) + deprecate match function Extend switch statement with pattern matching capability. Add support for discriminatory unions. (@SanderSpies, !1973 (merged))
• Destructuring in function parameters (@SanderSpies, !2002 (merged) + !2011 (merged))
• Ternary operator (@SanderSpies, !1993 (merged))
• Improve if else (#1456 (comment 1098253838)) (@SanderSpies, !1991 (merged))
• Check possibility to use return in switch statements. (@SanderSpies, !1995 (merged))

Modules

• Modules + syntax: replace import directives with proper JS like imports (@pewulfman + @SanderSpies for syntax: !2009 (merged))

Stdlib

• Add List.find_opt (@alistair.obrien , !1953 (merged))