This commit does not add or remove c’tors or d’tors, so it is *not* ABI-breaking.
If a c’tor/d’tor does nothing else than the default behavior, this commit replaces it with “= default”.
If an initializer list entry does nothing else than the default behavior, this commit removes it. First and foremost, remove default c’tor calls of base classes (always called by the compiler if no other base c’tor is explicitly called) and c’tor calls of members with complex types (e.g. “std::vector”).
In a few instances, user-defined copy c’tors / move c’tors / assignment operators / move assignment operators were replaced with “= default”, too. I only did this if I had a clear understanding of what’s going on.
The search for a matching importer had a few issues, see #3791. There were two different mechanisms to determine whether an importer accepts a specific file extension:
1. `aiImporterDesc::mFileExtensions`, which was forwarded to the UI via `BaseImporter::GetExtensionList()`.
2. `BaseImporter::CanRead()` when called with `checkSig == false`, which determines whether to actually use that importer.
Both were redundant and got out of sync repeatedly. I removed 2. completely and replaced it with 1., thereby syncing UI/import and shortening all `BaseImporter::CanRead()` implementations.
Further bugfixes:
- fixed glTF2 importer throwing exceptions when checking whether it can load a file
- removed `BaseImporter::SimpleExtensionCheck()` because it is no longer used and had a bug with case sensitivity
Since the `checkSig` parameter in `BaseImporter::CanRead()` is now useless, it can be removed completely. I’m not sure if this would break ABI compatiblity, so I’ll submit it with a later pull request.
