Enable annotation quoting for multi-line expressions

[charliermarsh]

Given:

x: DataFrame[
    int
] = 1

We currently wrap the annotation in single quotes, which leads to a syntax error:

x: "DataFrame[
    int
]" = 1

There are a few options for what to suggest for users here... Use triple quotes:

x: """DataFrame[
    int
]""" = 1

Or, use an implicit string concatenation (which may require parentheses):

x: ("DataFrame["
    "int"
"]") = 1

The solution I settled on here is to use the Generator, which effectively means we write it out on a single line, like:

x: "DataFrame[int]" = 1

It's kind of the "least opinionated" solution, but it does mean we'll expand to a very long line in some cases.

Closes #9136.

[MichaReiser]

Or, use an implicit string concatenation (which may require parentheses):

I wonder if that trips over static analysis tools.

The solution I settled on here is to use the Generator, which effectively means we write it out on a single line, like:

The main downside of this is that it undoes any formatting and the formatter won't be able to properly format the type annotation (except if we would parse it) on the next run, because it is now an unsplittable string. But I think it's a good enough solution to fix the bug.

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