Auto-generated markers in every output file

[ocornut]

In c6558176 I added a more visible header to the .cpp files:

// THIS FILE HAS BEEN AUTO-GENERATED BY THE 'DEAR BINDINGS' GENERATOR.
// **DO NOT EDIT DIRECTLY**
// https://github.com/dearimgui/dear_bindings

But was not sure how to add it to the main .h (going via the DOM writer).

I suppose it would make sense it will was added on all output files, either hardcoded in the code either via the template stuff.

[ShironekoBen]

The new template header stuff lets us put in common headers for all files, so I've put the warning message in there now.

[ocornut]

Looking great, thank you!