15.12.4.2: Clarify that a method's invocation type is used for varargs method

A DESCRIPTION OF THE PROBLEM :
Currently the section §15.12.4.2 of the JLS (https://docs.oracle.com/javase/specs/jls/se17/html/jls-15.html#jls-15.12.4.2) says:
> The final formal parameter of m necessarily has type T[]

This is slightly misleading because it seems to be the
> formal parameter **of the invocation type (§15.12.2.6)** of m

This can be seen with the following code snippet:
```
<T extends CharSequence> void printArgsType(T... args) {
    System.out.println(args.getClass());
}

printArgsType("a");
```
This prints `[Ljava.lang.String` instead of `[Ljava.lang.CharSequence`.