[issue] TAB should indent or complete [type=feature, module=core-21.5]

[Stephen J. Turnbull]

paul r writes:
 > > ISTR this being discussed on this list at some point in the past, but
 > >  don't remember the details.
 > 
 > I can't remember this, so I apologize if my suggestion has been
 > discussed many times.
 > Here is my own choice of behaviour for TAB key :
 >  - unless point is at the end of line, indent-according-to-mode
 >  - if point is at EOL :
 >    - unless line is indented according to mode, indent according to mode
 >    - if line is indented according to mode, complete
 > 
 > Classic use case would be : I'm typing a line, I start a new line,
 > type some code, hit TAB to have my line properly indented, carry on
 > typing, hit tab again to complete my symbol.
 > 
 > I've been using it for 3 years now, and I still like this behaviour a lot.
 > 
 >