Update ncurses to 20200118

Among the changes from before:

• Add support for extended colors on widechar version
• Enable ncurses extended functions
• Enable version 2 of the extended mouse support
• Enable SCREEN extensions

Modification that differs from upstream:

• _nc_delink_entries used to be exposed and was turn static, turn it back as dynamic to not break abi
• Adapt our old termcap.c to modern ncurses

MFC after: 3 weeks