Modified generation of the XyzAutoEditStrategy to more closely resemble
the procedure known from Eclipse editors:

a) A closing bracket/quote is only inserted automatically if it closes a
yet open bracket/quote pair (e.g., relevant for quoted strings when
manually typing the second quote where now no additional excess quote is
added).

b) When typing a closing bracket/quote manually and the following
character is the very same symbol, then the following symbol is replaced
instead of adding an additional excess closing bracket/quote. Increases
typing flow when manually typing the same content as was previously
generated automatically.

Fixed a few minor bugs in the process.