x/tools/gopls: use `static` modifier for unexported function/method semantic tokens

[segevda]

Suggesting to use the static modifier for function / method semantic tokens. This will allow finer grained color customization:

This customization exists in proprietary IDE's like JetBrains GoLand, and can later be expanded to distinguish unexported types/variables/consts/etc from exported ones.

[findleyr]

CC @pjweinb

[pjweinb]

This is a plausible improvement. I'll take a look.

[segevda]

This is a plausible improvement. I'll take a look.

Thanks @pjweinb . If you find that this is doable, I will be happy to implement the change.

[pjweinb]

(this may be a duplicate; i thought i responded, but it's not here)
The Go language identifies exported (non-static) variables with capitalization, so for most purposes this proposal doesn't add information, although it would make the display more colorful. The place where it would add information is that capitalized variables local to functions or function signatures would be marked static (non-exported). These are rare. To the extent all that is true, I don't think it's worth touching the code at this time, but it would be worth adding a comment to the code, for the next time there's an extensive change, that all non-exported variables should have a 'static' modifier.