* maint:
  Update test suite
  Also unwrap map_type_* name and value
  Add unwrap calls to map_field_* in erl_syntax

* zadean/syntax_tools/add_missing_unwrap/OTP-16012/PR-2348:
  Update test suite
  Also unwrap map_type_* name and value
  Add unwrap calls to map_field_* in erl_syntax

This adds missing calls to unwrap/1 for the map_field_* name and value functions and puts them inline with map_expr_fields/1.
Using these functions with "wrapped" nodes fails with badarg.

'cond' expressions were an experimental addition to the Erlang language
that never matured to the point that it could be incorporated to it.

This pull request takes out the (incomplete anyway) handling of 'cond'
expressions from the syntax_tools application, so as to simplify its
code base.

* maint:
  syntax_tools: Fix pretty-printing of type funs

See also ERL-815.

* maint:
  erts: Add comment about [] and nil() to The Abstract Format
  syntax_tools: Correct erl_syntax:revert/1

* hasse/syntax_tools/fix_revert/OTP-15294:
  erts: Add comment about [] and nil() to The Abstract Format
  syntax_tools: Correct erl_syntax:revert/1