Replace filenames in reflection with filenames+includes.

[CasperN]

Adding the map of schema files to included schemas to reflection.
This feature was requested at the end of #6613.
I made a backwards incompatible change to fbs_files since it was added recently.
Also related: #6428.

@mikkelfj

[mikkelfj]

Can't speak to the implementation, but I am happy with the schema change in reflection.fbs.

I'm a bit concerned about the already implementated convetntion of having filenames being relative to the flatc invocation path by default. It could unintentionally leak information and is likely a relative path starting with '..' if invoked in a typically build environment where the build directory is separate from the source tree.

I'd suggest using the directory holding the root fbs file as the default relative path. (This assuming that multiple cli specified fbs files are not merged into a single bfbs file).

[CasperN]

convention of having filenames being relative to the flatc invocation

Its actually relative to a specified "project root", passed in by passing a --bfbs-filenames=$project_root flag. Defaulting to the relative to the first filename isn't a bad idea, although there's no guarantee that later filenames wouldn't have a "..".

[mikkelfj]

Defaulting to the relative to the first filename isn't a bad idea, although there's no guarantee that later filenames wouldn't have a "..".

But that would be OK in that case.