No, you don't need to style it like that for performance reasons. Write it for readability. Bundling and minification will handle the performance part.
Yes, bundling and minification works in Webforms. Here are key steps from the post Adding Bundling and Minification to Web Forms:
Create your bundle:
using System.Web.Optimization;
public class BundleConfig
{
public static void RegisterBundles(BundleCollection bundles)
{
bundles.Add(new ScriptBundle("~/bundles/jquery").Include(
"~/Scripts/jquery-{version}.js"));
//...
Register your bundle: (global.asax)
void Application_Start(object sender, EventArgs e)
{
BundleConfig.RegisterBundles(BundleTable.Bundles);
//...
Reference your bundle: (masterpage)
<asp:PlaceHolder runat="server">
<%: Scripts.Render("~/bundles/jquery") %>
</asp:PlaceHolder>
Get bundling and minification from NuGet.