Coercion hint: suggestion that doesn't compile after a parenthesized operand, and the hint names the expanded type #9105

Found by a bug hunt over the 16 commits from eb087382 to cd641cbc.

A hint that doesn't compile.

type a = {x: int, y: int}
type b = {x: int}
let v: a = {x: 1, y: 2}
let w: b = v->(r => r)

The error is reported at 4:12-21, which leaves out the final ). The hint suggests v->(r => r :> b), and applying it fails with "Type 'a => 'a is not a subtype of b". A suggestion that compiles is (v->(r => r) :> b). The rewrite is built from Parser.extract_text_at_loc loc, so it inherits the truncated location.

The hint names the expanded type.

let f = (x: Generator.t<'a, unit, unit>): Iterable.t<'a> => x

The message says the expected type is Iterable.t<'a> (defined as iterable<'a>), but the hint suggests (x :> iterable<'a>). That compiles, but it doesn't name the type the message shows. The target comes from the expanded element of the trace pair (error_message_utils.ml#L774-L779).

Both reproduce at b123b7c3. Related: #9037.

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