This was a regression from #7435 which introduced threads and caused JNI
to misbehave and fail to load our expected classes. Provide a workaround
based on the description in https://stackoverflow.com/a/16302771 which
stores a main thread's class loader and uses that in neighbouring
threads.
Clang-format sees the text behind `#pragma region` as code and formats it. Instead of stating the copyright and date there, it's now in the comment block right below it. The text "Copyright" is left in the `#pragma region` line, as clang-format sees it as a single identifier.
I took the opportunity to normalize the dates, and add the copyright notice to the source files where it was missing them (except for third-party and the generated resources.h file).
