Rename type parameters that shadow an enclosing type parameter

Renames a type parameter that shadows one of an enclosing class, interface, record or method, choosing the next conventional single-letter name the file does not use, such as U or V, or a numeric suffix up to 9 when none is free, and updates its references and Javadoc @param tag. One whose name also denotes something else in its declaration, with no free name, or outside Java source is left alone.