Replace strcpy and strcat with safer alternatives in C-code on Android

[Jacalz]

Checklist

• I have searched the issue tracker for open issues that relate to the same feature, before opening a new one.
• This issue only relates to a single feature. I will open new issues for any other features.

Is your feature request related to a problem?

The functions strcpy and strcat are generally regarded as unsafe as they do not check the length of the buffer they are writing into. I don't know if the current uses in https://github.com/search?q=repo%3Afyne-io%2Ffyne%20strcpy&type=code and https://github.com/search?q=repo%3Afyne-io%2Ffyne%20strcpy&type=code can be abused in any way (I couldn't see something strange at first glance) but it does not hurt to stay on the safe side.

We should try to replace these with strlcpy and strlcat respectfully assuming that they exist.

Is it possible to construct a solution with the existing API?

Yes, assuming that the improved APIs exist in the Android c-library.

Describe the solution you'd like to see.

Replace functions with strlcat and strlcpy to avoid potential issues with writing outside of buffers.

[Jacalz]

We should likely also replace strdup with strndup for extra safety: https://github.com/search?q=repo%3Afyne-io%2Ffyne+strdup&type=code