gopls/internal/goasm: add Hover for assembly files

[groot-guo]

Dispatch file.Asm in server.Hover to goasm.Hover, which finds the
identifier under the cursor and reports its name and kind (text,
global, data, ref, label).

Updates golang/go#71754

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[gopherbot]

Message from Gopher Robot:

Patch Set 1:

(1 comment)

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[gopherbot]

Message from 郭根源（genyuan）:

Patch Set 2:

(1 comment)

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[gopherbot]

This PR (HEAD: 8df9d83) has been imported to Gerrit for code review.

Please visit Gerrit at https://go-review.googlesource.com/c/tools/+/798760.

Important tips:

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[gopherbot]

Message from Alan Donovan:

Patch Set 2:

(2 comments)

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