[ error ] Improve error messages for Delay &co

[dunhamsteve]

Description

This PR improves error messages in Delay statements to address #3036. It adds a check for an additional simpleExpr after the statement. It also introduces a mustFailBecause helper function that will fail with a message if a given parser succeeds at the current point.

Prior to this change, the following code:

module DelayParse

public export
data MyStream : Type where
  (::) :  (anA : a)
       -> (nextA : a -> a)
       -> Inf MyStream
       -> MyStream

public export
go : a -> (a -> a) -> MyStream
go initA fn =
  MyStream.(::) initA fn (Delay (fn initA) fn)

would fail with:

1/1: Building tests.idris2.perror029.DelayParse (tests/idris2/perror029/DelayParse.idr)
Error: Not the end of a block entry, check indentation.

tests.idris2.perror029.DelayParse:13:26--13:27
 09 |
 10 | public export
 11 | go : a -> (a -> a) -> MyStream
 12 | go initA fn =
 13 |   MyStream.(::) initA fn (Delay (fn initA) fn)
                               ^

and now we get:

1/1: Building DelayParse (DelayParse.idr)
Error: Delay only takes one argument.

DelayParse:13:44--13:46
 09 | 
 10 | public export
 11 | go : a -> (a -> a) -> MyStream
 12 | go initA fn =
 13 |   MyStream.(::) initA fn (Delay (fn initA) fn)
                                                 ^^

[gallais]

Sorry about the missclick. I wanted to say that I suspected this PR
would arrive when I mentioned the fact the parser was the problem. :)