The fundamental bug causing TestChangePackageName to fail has been
fixed, yet unskipping it revealed a new bug: tracking whether or not a
package should be loaded requires that we actually store that package in
s.meta. In cases where we drop metadata, we also lose the information
that a package path needs to be reloaded.

Fix this by significantly reworking the tracking of pending loads, to
simplify the code and separate the reloading logic from the logic of
tracking metadata. As a nice side-effect, this eliminates the needless
work necessary to mark/unmark packages as needing loading, since this is
no longer tracked by the immutable metadata graph.

Additionally, eliminate the "shouldLoad" guard inside of snapshot.load.
We should never ask for loads that we do not want, and the shouldLoad
guard either masks bugs or leads to bugs. For example, we would
repeatedly call load from reloadOrphanedFiles for files that are part of
a package that needs loading, because we skip loading the file scope.
Lift the responsibility for determining if we should load to the callers
of load.

Along the way, make a few additional minor improvements:
 - simplify the code where possible
 - leave TODOs for likely bugs or things that should be simplified in
   the future
 - reduce the overly granular locking in getOrLoadIDsForURI, which could
   lead to strange races
 - remove a stale comment for a test that is no longer flaky.

Updates golang/go#53878

Change-Id: I6d9084806f1fdebc43002c7cc75dc1b94f8514b9
Reviewed-on: https://go-review.googlesource.com/c/tools/+/417576
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This test ran slowly sometimes. Now that we have improved performance,
elimininated arbitrary timeouts, and improved cacheability of
computed results when running with -short, I suspect this test should no
longer flake.

If it does, we can reduce its cost in other ways rather than turning it
off entirely.

Updates golang/go#48773
Updates golang/go#53878

Change-Id: I878e78117df5a1a25f4ac5f72e02f28fc078ec73
Reviewed-on: https://go-review.googlesource.com/c/tools/+/419106
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This test was originally skipped due to deadline exceeded errors. In the
time since, we've made performance improvements, fixed races, and
altered the regtests to remove arbitrary deadlines. Unskip it to see if
it still flakes.

For golang/go#44098
For golang/go#53878

Change-Id: I06530f2bc9c6883f415dc9147cfcbf260abb2a00
Reviewed-on: https://go-review.googlesource.com/c/tools/+/418898
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I believe the races described in the issue have been fixed: we should
invalidate mod tidy results on any metadata change. If this invalidation
doesn't work due to a race, we want to know about it.

Update the test to wait for file-related events to complete before
removing files, in an attempt to avoid windows file-locking issues.

For golang/go#40269
For golang/go#53878

Change-Id: I91f0cb4969851010b34904a0b78ab9bd2808f92e
Reviewed-on: https://go-review.googlesource.com/c/tools/+/420718
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Metadata reloading has been significantly refactored recently. Unskip
this test to see if it still flakes.

For golang/go#51352
For golang/go#53878

Change-Id: I9f2ae1835bbace1b5095c2d45db082c4e709437b
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Reloading has been significantly refactored recently. Unskip this test
to see if it flakes:
 - If it does not flake, that is a useful signal.
 - If it does flake, that is also a useful signal.

Notably, following CL 419500 we allow network when reloading the
workspace, and so do not need to apply quick-fixes in order to download
the new module from the proxy.

For golang/go#46375
For golang/go#53878

Change-Id: Idde7195730c32bdb434a26b28aac82649dd1b5ac
Reviewed-on: https://go-review.googlesource.com/c/tools/+/422910
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Remove skips for two tests related to line directives (now fixed), and
delete a test related to the old parse cache, which no longer exists.

Updates golang/go#53878

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This test was fixed in CL 494675, which forced snapshots to observe all
overlays when updating the view.

Updates golang/go#53878
Fixes golang/go#57934

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This test is updated to exercise hover over literals, not vars, as was
decided in golang/go#58220.

Updates golang/go#53878

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