ConstantDynamic common bootstrap methods

Consider adding a selection of commonly useful bootstrap methods for returning constant values, such as for:

- loading a primitive class (e.g. int.class)

- loading a primitive value smaller that int (boolean, byte, char and short)

- loading a default value of a given type (null, zero, value-type default)

- loading a named (static final) constant from a class, or (as a special case) an enum member

- loading a regex Pattern

- loading a VarHandle

- loading a value returned from a factory method or perhaps invokers that are method handle based (so a resulting method handle from a combinatorial operation or a transformation is a constant).

- as a special case of factories, computing List.of, Map.of, Set.of on a list of constants


Certain bootstrap methods may be required for the constant folding language and intrinsic support for ldc and invokedynamic (see JDK-8178320).