Generate code in SwitchBootstraps.generateTypeSwitch that require fewer adaptations

When bootstrapping switches we currently add a call to Objects.checkIndex by adding a filterArgument to the method handle, then explicitCast to adapt the code to the right type. These operations means a not insignificant number of LF and species classes are needed to be spun up when bootstrapping even a relatively simple runtime-bootstrapped switch.

By folding the checkIndex code and generating the method with precise arguments from the start we can avoid a few MH transforms and associated class spinning, while retaining parity on throughput metrics.