internal/robustio: move robustio

Moves gopls/internal/robustio to internal/robustio.
Allows usage by packages in x/tools outside of gopls.

Change-Id: I71743c3a91458b77f12606b743b5de7e23cc5051
Reviewed-on: https://go-review.googlesource.com/c/tools/+/460116
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Alan Donovan <[email protected]>
Run-TryBot: Tim King <[email protected]>
gopls-CI: kokoro <[email protected]>

Author: timothy-king

gopls/internal/lsp/fake/sandbox.go

@@ -13,8 +13,8 @@ import (
 	"path/filepath"
 	"strings"
 
-	"golang.org/x/tools/gopls/internal/robustio"
 	"golang.org/x/tools/internal/gocommand"
+	"golang.org/x/tools/internal/robustio"
 	"golang.org/x/tools/internal/testenv"
 	"golang.org/x/tools/txtar"
 )

gopls/internal/lsp/fake/workdir.go

@@ -19,8 +19,8 @@ import (
 	"time"
 
 	"golang.org/x/tools/gopls/internal/lsp/protocol"
-	"golang.org/x/tools/gopls/internal/robustio"
 	"golang.org/x/tools/gopls/internal/span"
+	"golang.org/x/tools/internal/robustio"
 )
 
 // RelativeTo is a helper for operations relative to a given directory.

gopls/internal/lsp/filecache/filecache.go

@@ -31,7 +31,7 @@ import (
 	"sync/atomic"
 	"time"
 
-	"golang.org/x/tools/gopls/internal/robustio"
+	"golang.org/x/tools/internal/robustio"
 )
 
 // Get retrieves from the cache and returns a newly allocated