Add ToolProvider information to jdk.jpackage API docs

The following should be added to the javadoc comments for the jdk.jpackage module:


 * <p> This module provides the equivalent of command-line access to <em>jpackager</em>
 * via the {@link java.util.spi.ToolProvider ToolProvider} SPI.
 * Instances of the tool can be obtained by calling
 * {@link java.util.spi.ToolProvider#findFirst ToolProvider.findFirst}
 * or the {@link java.util.ServiceLoader service loader} with the name
 * {@code "jpackage"}.


There are similar comments describing the "javac", "jlink", and "jmod" tools.