Add a section to the documentation about well-known issues with non-standard Modelica code

[casella]

This ​report shows what happens when the NF is switched on by default. There are 1000 improvements, but also more than 600 regressions. Most of them take place in old libraries that contained illegal Modelica code, so they can be used to sample the most commonplace istances of such a problem.

OpenModelica is tried out by more and more new potential users, which may encounter failures which are not due to OMC shortcomings, but rather to non-standard Modelica code. We should add a section to the documentation that describes the most common situations and how to fix them.

[casella]

In case of errors which are likely caused by violations of the Modelica specification we should add a specific message to the compiler error, such as

Non-array modification ‘4‘ for array component ‘p‘, possibly due to missing ‘each‘.
This error is possibly due to non-standard Modelica code, see the User Guide <link>

that refer the user to the section of the User Guide that explains the whole story.

[casella]

See ​PR 7130

[adrpo]

Found another bad one today. This one doesn't even parse in spec compliant tools:
​https://github.com/MarekMatejak/Physiolibrary/issues/33

[casella]

PR 7130 updated accordingly.

[casella]

Merged in ​aae2bf0.