Clarify path param naming (#32969)

In history (from some legacy frameworks), both `:name` and `name` are
supported as path path name, `:name` is an alias to `name`.

To make code consistent, now we should only use `name` but not `:name`.

Also added panic check in related functions to make sure the name won't
be abused in case some downstreams still use them.

routers/web/repo/issue_list.go

@@ -748,7 +748,7 @@ func issues(ctx *context.Context, milestoneID, projectID int64, isPullOption opt
 
 // Issues render issues page
 func Issues(ctx *context.Context) {
-	isPullList := ctx.PathParam(":type") == "pulls"
+	isPullList := ctx.PathParam("type") == "pulls"
 	if isPullList {
 		MustAllowPulls(ctx)
 		if ctx.Written() {