x/tools/gopls: kubernetes' vendored modules are opened as new views

[findleyr]

While testing zero-config gopls (#57979), I noticed that jumping to definition on a vendored Kubernetes module creates a new View for that module. This could result in increased memory usage, and partial references results.

We should not create Views for vendored modules. The fix seems very straightforward, so we should fix this for v0.15.0.

[gopherbot]

Change https://go.dev/cl/565458 mentions this issue: gopls/internal/cache: don't create Views for vendored modules

[gopherbot]

Change https://go.dev/cl/565695 mentions this issue: [gopls-release-branch.0.15] gopls/internal/cache: don't create Views for vendored modules