x/tools/gopls: a new internal diff implementation

[findleyr]

This is a tracking issue for landing https://go.dev/cl/396855, implementing a new internal diff algorithm to reduce our external dependencies.

(I will file a separate umbrella issue for the entire process of making this switch. This issue exists for milestone tracking).

[mvdan]

Is the CL link wrong? I see:

internal/lsp: add an option to get notified of bug reports

[findleyr]

Is the CL link wrong?

Whoops, indeed! Fixed. Thanks.

[gopherbot]

Change https://go.dev/cl/396855 mentions this issue: internal/lsp/diff: new diff implementation to replace go-diff