When enabling all experiments (done by VS Code nightly), switch to the
checked version of the new diff implementation.

Also remove some experimental settings that are now on by default.

Updates golang/go#52967

Change-Id: Id272c4a646006a739e49d48f0f09b2f8b0982bab
Reviewed-on: https://go-review.googlesource.com/c/tools/+/419981
gopls-CI: kokoro <noreply+kokoro@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
Reviewed-by: Peter Weinberger <pjw@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

We've been using this setting in experimental for some time without
issue, so switch it to default.

For golang/go#52967

Change-Id: Ib4d786e689d4b0f009195cc86d7dd5d8269cf424
Reviewed-on: https://go-review.googlesource.com/c/tools/+/427534
Reviewed-by: Peter Weinberger <pjw@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
gopls-CI: kokoro <noreply+kokoro@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

As the next step in the diff migration, stop running both diffs by
default.

For golang/go#52967

Change-Id: I4b1a434d13f4349feabc5eb0daf3b9e8d56f99aa
Reviewed-on: https://go-review.googlesource.com/c/tools/+/520135
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Peter Weinberger <pjw@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
gopls-CI: kokoro <noreply+kokoro@google.com>

For golang/go#52967

Change-Id: I3afdeffa739311942795389bf2607c942bd8fc68
GitHub-Last-Rev: f95ca66
GitHub-Pull-Request: #465
Reviewed-on: https://go-review.googlesource.com/c/tools/+/548175
Reviewed-by: Robert Findley <rfindley@google.com>
Auto-Submit: Robert Findley <rfindley@google.com>
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Reviewed-by: Bryan Mills <bcmills@google.com>
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CL 548175 removed the sergey/diffmatchpatch diff implementation,
which had been disabled by default for some time.

This change removes the dependency from gopls to the myers
implementation, and the associated configuration plumbing
for alternative implementations. The myers implementation
was not actually used because the GoDiff=true default
in Hooks (see default.go) was always overridden.

Unfortunately we cannot yet delete the myers implementation
completely because the marker tests depend on the details
of its behavior. A follow-up change should apply the diff
and compare the result, instead of comparing diffs.

Fixes golang/go#52967

Change-Id: I67796e260ac00f7edc31ce18fda7b1042e8374f8
Reviewed-on: https://go-review.googlesource.com/c/tools/+/548856
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Robert Findley <rfindley@google.com>