Add methods to Character.UnicodeBlock (returning first & last codepoints, the list of blocks)

The following methods seems very helpful for developers who handle Unicode blocks. They should be added to JDK.

- int getFirstCodePoint() - returns the first code point of the block
- int getLastCodePoint() - returns the last code point of the block
- UnicodeBlock[] getAllBlocks() or something - returns all UnicodeBlocks