Report more "unexpected bare value" errors

[jez]

Motivation

While helping a user attempt to write some code today, I noticed that they had
this in their code and it did the right thing statically but only worked at
runtime because generics are erased (T::Array[x]). Had they attempted to do
something similar with T.class_of or T.any or something else, it would not
have done the thing they hoped it would have.

Ideally an even better error message would include something like an autocorrect
like "Did you meant to explicitly annotate this value's type here?" and offer to
replace x in the test with T.type_parameter(:U), or whatever the type of x
is. That isn't always going to be the right suggestion, but it will at least get
the user closer to understanding what the problem is.

Test plan

See included automated tests.

[jez]

We have a policy of testing changes to Sorbet against Stripe's codebase before
merging them. I've kicked off a test run for the current PR. When the build
finishes, I'll share with you whether or how it failed. Thanks!

Stripe employees can see the build results here:

→ https://go/builds/bui_Q6f3GZMJfpyBAv
→ https://go/builds/bui_Q6f3FuQSzgatfj
→ https://go/builds/bui_Q6f3iBy7i1Dkg2