Fix incorrect relative/absolute URL usages (#29531)

Add two "HTMLURL" methods for PackageDescriptor. 
And rename "FullWebLink" to "VersionWebLink"

routers/web/user/package.go

@@ -163,7 +163,7 @@ func RedirectToLastVersion(ctx *context.Context) {
 		return
 	}
 
-	ctx.Redirect(pd.FullWebLink())
+	ctx.Redirect(pd.VersionWebLink())
 }
 
 // ViewPackageVersion displays a single package version