Whitespace sensitive parsing of local definitions (type-ascribing let)

[ohad]

Might be related to #113 .

Steps to Reproduce

$ cat Bar.idr 
X : Nat
X = let a : Nat
        a = 0
        in a
$ idris2 -c Bar.idr 

Expected Behavior

1/1: Building Bar2 (Bar.idr)
$

Observed Behavior

Bar.idr:4:9--4:9:Parse error: Couldn't parse declaration (next tokens: [in, identifier a, end of input])

If we dis-indent the in keyword, it parses fine:

$ cat Bar2.idr 
X : Nat
X = let a : Nat
        a = 0
       in a
$ idris2 -c Bar2.idr 
1/1: Building Bar2 (Bar2.idr)
$