Invokers.callSiteForm only depend on the MethodTypeForm and link type, and can be generated ahead of time by jlink --generate-jli-classes

We generate at least some of these during bootstrap in many applications - 6 forms are recognized by the simple HelloClasslist app we use for training runs - and thus generating these ahead-of-time speeds up startup and should enable other startup optimization techniques (such as CDS and AOT) to allow for faster code execution off the bat.