textproc/libunibreak: update to 5.1

New in libunibreak 5.1

• Speed up line-break property lookup
• Update the data to conform to Unicode 15

New in libunibreak 5.0

• Update the data to conform to Unicode 14
• Add per_code_point variants of utf8 and utf16 functions
• Do not always break after the last character
• Clean up code and test