Add go.mod file for pkg.go.dev support?

[trevorade]

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Comment

We would expect to start seeing v0.0.0 or similar at:

https://pkg.go.dev/github.com/microsoft/TypeScript?tab=versions

Presumably, 7.1 will be v71.0.0.

At the moment, in Google, we can't pull in any nightlies until this happens.