gopls: add scheme to CodeDescription.href

### gopls

- Add `https` scheme to `CodeDescription.href`

According to the [LSP specification](https://microsoft.github.io/language-server-protocol/specification#diagnostic), `CodeDescription.href` must be [URI type](https://microsoft.github.io/language-server-protocol/specification#uri). As described in the [RFC](https://tools.ietf.org/html/rfc3986#section-3), the scheme is required for URI:

> The scheme and path components are required, though the path may be empty (no characters).

Current `gopls` does not add the scheme to `CodeDescription.href`, and this results in some LSP clients ([at least this client](https://github.com/autozimu/LanguageClient-neovim)) which are strictly validating the URI format to be failed to populate diagnostics.

Change-Id: I73f01c2e97ed1adb62fbed451a7c9b0c9794b66a
GitHub-Last-Rev: 6985bfe
GitHub-Pull-Request: #277
Reviewed-on: https://go-review.googlesource.com/c/tools/+/294569
Reviewed-by: Rebecca Stambler <[email protected]>
Trust: Rebecca Stambler <[email protected]>
Trust: Robert Findley <[email protected]>
Run-TryBot: Rebecca Stambler <[email protected]>
gopls-CI: kokoro <[email protected]>
TryBot-Result: Go Bot <[email protected]>

Author: 110y

internal/lsp/cache/errors.go

@@ -14,6 +14,8 @@ import (
 	"strconv"
 	"strings"
 
+	errors "golang.org/x/xerrors"
+
 	"golang.org/x/tools/go/analysis"
 	"golang.org/x/tools/go/packages"
 	"golang.org/x/tools/internal/analysisinternal"
@@ -23,7 +25,6 @@ import (
 	"golang.org/x/tools/internal/lsp/source"
 	"golang.org/x/tools/internal/span"
 	"golang.org/x/tools/internal/typesinternal"
-	errors "golang.org/x/xerrors"
 )
 
 func sourceDiagnostics(ctx context.Context, snapshot *snapshot, pkg *pkg, severity protocol.DiagnosticSeverity, e interface{}) ([]*source.Diagnostic, error) {
@@ -167,7 +168,7 @@ func sourceDiagnostics(ctx context.Context, snapshot *snapshot, pkg *pkg, severi
 
 func typesCodeHref(snapshot *snapshot, code typesinternal.ErrorCode) string {
 	target := snapshot.View().Options().LinkTarget
-	return fmt.Sprintf("%s/golang.org/x/tools/internal/typesinternal#%s", target, code.String())
+	return fmt.Sprintf("https://%s/golang.org/x/tools/internal/typesinternal#%s", target, code.String())
 }
 
 func suggestedAnalysisFixes(snapshot *snapshot, pkg *pkg, diag *analysis.Diagnostic) ([]source.SuggestedFix, error) {