Meta issue for syntax improvements in Pulse

[aseemr]

• [x] fn (p:int -> int) ... doesn't parse, it has to be written as fn (p:(int -> int)) ... (note the extra parenthesis around the arrow)
• [x] let _ : t = e; doesn't parse, it has to be written as let _u : t = e
• [x] refinement types annotation x:int { p x } doesn't work, it has to be written as x:(x:int { p x })

[nikswamy]

Fixed in 5c18b713a891323d828a5591fd6e2c7c4f00af16