Parse errors should display text being parsed

(More general form of part of #3805 (closed))

Typical parse error:

TestErr.hs:1:0: Invalid type signature

Typical type error:

TestErr.hs:2:6:
    Couldn't match expected type `Int' against inferred type `[Char]'
    In the expression: "x"
    In the definition of `foo': foo = "x"

That explicit description of which expression was being examined is frequently useful in quickly understanding an error that occurs in the middle of a complex piece of code. There's no obvious reason why we can't have the same sort of thing on all parse errors - a quick glance at the parser suggests it's already tracking the byte range, so it should be fairly straightforward. I'd like to see this (on all parse errors, not just this one):

TestErr.hs:1:0:
    Invalid type signature
    While trying to parse: `foreign export ccall foo :: IO ()'

Trac metadata

Trac field	Value
Version	6.12.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler (Parser)
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