Fix locations of shadowing warnings in ms_transform

A shadowed variable in an ms_transform match expression emits a warning
located at the match expression instead of the variable.
Fix miscompilation when module contains multiple named funs

A module containing two named funs bearing the same name and arity could be
miscompiled.

Reported-by: Sam Chapin
Remove comments about unicode atoms in OTP 18

There was once a plan to implement support for unicode atoms in OTP
18. This plan has been stopped until further notice, and the
information about this is now removed from the documentation.
Merge branch 'nox/compiler/eep37-duplicate-names/OTP-12262' into maint

* nox/compiler/eep37-duplicate-names/OTP-12262:
  Fix miscompilation when module contains multiple named funs
Merge branch 'nox/stdlib/ms_transform-locate-shadow-warning/OTP-12264' into maint

* nox/stdlib/ms_transform-locate-shadow-warning/OTP-12264:
  Fix locations of shadowing warnings in ms_transform
Merge branch 'siri/no-unicode-atoms/OTP-12172' into maint

* siri/no-unicode-atoms/OTP-12172:
  Remove comments about unicode atoms in OTP 18