The lexer needs its own lexerState, before it was using
the syntax highlighter user state. This breaks the brace
depth calculation of the highlighter.

Reviewed-by: Roberto Raggi

Task-number: QTCREATORBUG-1825

Task-number: QTCREATORBUG-1818

Done-with: Thomas Hartmann

Task-number: QTCREATORBUG-1816

Fixes incorrect indentation we got previously when they were used in a
statement context.

So you now get
enum A { a = 2,
         b = 3,
       };

This will allow much faster indenting of selected areas as the state
doesn't have to be checked again for every line.

Keep more information by using enter() instead of turnInto() when moving
from a *_start to *_open.

Done-with: Erik Verbruggen