Allow return type in conditional if body is followed by a colon

[jakebailey]

This modifies my logic in #47550 allow an arrow function with a return type so long as that arrow function is immediately followed by another colon, which is instead chosen to terminate the conditional expression.

Fixes #48733

[jakebailey]

@typescript-bot pack this

[typescript-bot]

Heya @jakebailey, I've started to run the tarball bundle task on this PR at 2398762. You can monitor the build here.

[typescript-bot]

Hey @jakebailey, I've packed this into an installable tgz. You can install it for testing by referencing it in your package.json like so:

{
    "devDependencies": {
        "typescript": "https://typescript.visualstudio.com/cf7ac146-d525-443c-b23c-0d58337efebc/_apis/build/builds/124798/artifacts?artifactName=tgz&fileId=12EB9E2D14C16ED79A119CECACDDB29A6E0083AEC272E7D2968EE4340320600D02&fileName=/typescript-4.7.0-insiders.20220420.tgz"
    }
}

and then running npm install.

---

There is also a playground for this build and an npm module you can use via "typescript": "npm:@typescript-deploys/pr-build@4.7.0-pr-48788-2".;

[jakebailey]

Demo: Playground Link

[sandersn]

This change is intended for 4.8, right?
At least, I thought we decided to revert the original change at a design meeting (or you recommended and we've been waiting to talk about it there).

[jakebailey]

Yes, 4.8, given we took too long to make a decision. There's a revert PR for the original fix I made (#48940) and I'll rebase these three PRs to make them correct again.

[sandersn]

This looks like it does what it says, although I recall that we wanted to parse JS in a spec-compliant way. Does this need a follow-up PR for that?

[jakebailey]

Sorry, yes, I don't have the final fix yet. Likely this PR does what we want, but I need to really check.