C operator mode could consistently be applied to the text in the editor

[codemanyak]

Issue #872 led to the introduction of a mere display switch (via menu toggle item and a toggle button in the toolbar). This was sound, easy to implement and free of risks. The syntax rules for the input remained the same.

In a way, we might try to extend this one-way conversion to a reversible one and

1. allow to enter the text in C operator syntax in the editor (while the C operator mode is active), converting the text to Structorizer syntax on committing;
2. fill the editor text field with the element text converted to C operator syntax (if C operator mode is active).

Originally posted by @codemanyak in #872 (comment)

[codemanyak]

Combined assignment operators ( ++, --, +=, -=, *=, etc.) a user might enter are likely to cause major conversion problems, though.
So this is rather a long-term proposal, possibly to be postponed beyond the impementation of #800.

[codemanyak]

It should be mentioned that this enhancement tends to complicate the Content Assist introduced on behalf of #1066, and vice versa.