internal/lsp/cache: set a 15 minute deadline on calls to packages.Load
internal/lsp/cache: set a 15 minute deadline on calls to packages.Load

We've recently noticed multiple instances of `go list` hanging
indefinitely during an initial workspace load. Heschi suggested setting
a 5 minute deadline on the IWL, but it seems reasonable to set this
deadline on all calls to packages.Load since that calls `go list`.

I also started with a 15 minute deadline to be a little more careful.
Do you think this is risky enough to merit an experimental setting?

Fixes golang/go#42132

Change-Id: I0a38741f3d99b6a38c46c3e663daf61f2cb45581
Reviewed-on: https://go-review.googlesource.com/c/tools/+/266478
Trust: Rebecca Stambler <d7cf11e5f299d88ea8348366a9fc4f7c335c3afa@golang.org>
Run-TryBot: Rebecca Stambler <d7cf11e5f299d88ea8348366a9fc4f7c335c3afa@golang.org>
gopls-CI: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
TryBot-Result: Go Bot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Heschi Kreinick <e89ab2b172855aa0ad01c40c4d8a3535a61ac68a@google.com>

golang/tools,golang/tools,golang/tools,golang/tools,golang/tools