OpenSystemsDevelopment / qpdf

- Added `validate()` invocation to `m->embedded_files`.
- Introduced `value_validator` to ensure only dictionaries are accepted in `EmbeddedFiles`.
- Enabled consistent value validation and key validation logic.

…rove memory management, and simplify initialization logic.

…cess for consistency and readability.

Using search and replace.

Remove any ambiguity around whether old or new value is being
returned.

Change .clang-format and commit automated changes from a fresh run of
format-code

Run this:

for i in  **/*.cc **/*.c **/*.h **/*.hh; do
  clang-format < $i >| $i.new && mv $i.new $i
done