Give better error message if ; after tikzmath function definition is missing

[user202729]

Brief outline of the proposed feature

Currently if a function declaration in tikzmath command does not have the trailing ;, the error message is incomprehensible.

I think that compared to C style programming languages, it is not common to expect a function declaration (unlike struct declaration) to have a trailing ;.

It would be better to give a better error message than the current behavior (the current behavior is highly dependent on what follows it)

Usage example

No response