This attribute is not a URI; it is just the filename without its
parent directory path. To avoid confusion, let's rename it to
"filename", leaving the struct without a "uri" attribute.
No longer allocate it as a "VarSize". This used to be a clever trick
to save memory 10 years ago, but these days, keeping the code
maintainable seems more important than saving a few kilobytes of
memory.
Since we switched from autotools to Meson in commit
94592c1406, we don't need to include
`config.h` early to properly enable large file support. Meson passes
the required macros on the compiler command line instead of defining
them in `config.h`.
This means we can include `config.h` at any time, whenever we want to
check its macros, and there are no ordering constraints.
