gh-74902: Add Unicode Grapheme Cluster Break algorithm (GH-143076)

Add the unicodedata.iter_graphemes() function to iterate over grapheme
clusters according to rules defined in Unicode Standard Annex #29.

Add unicodedata.grapheme_cluster_break(), unicodedata.indic_conjunct_break()
and unicodedata.extended_pictographic() functions to get the properties
of the character which are related to the above algorithm.

Co-authored-by: Guillaume "Vermeille" Sanchez <guillaume.v.sanchez@gmail.com>