This is required for downstream Rust dependencies to properly import
libraries using `extern crate`.

- Adds a `crate_type` kwarg to library targets, allowing the different
  types of Rust [linkage][1].
- Shared libraries use the `dylib` crate type by default, but can also
  be `cdylib`
- Static libraries use the `rlib` crate type by default, but can also
  be `staticlib`
- If any Rust target has shared library dependencies, add the
  appropriate linker arguments, including rpath for the sysroot of the
  Rust compiler

[1]: https://doc.rust-lang.org/reference/linkage.html

Also add new tests for the platform-specific and compiler-specific
versioning scheme.

A rough summary is:

1. A bug in how run_tests.py:validate_install checked for files has been
   fixed. Earlier it wasn't checking the install directory properly.
2. Shared libraries are no longer installed in common tests, and the
   library name/path testing is now done in platform-specific tests.
3. Executables are now always called something?exe in the
   installed_files.txt file, and the suffix automatically corrected
   depending on the platform.
4. If a test installs a file called 'no-installed-files', the installed
   files for that test are not validated. This is required to implement
   compiler-specific tests for library names/paths such as MSVC vs MinGW
5. The platform-specific file renaming in run_tests.py has been mostly
   removed since it is broken for shared libraries and isn't needed for
   static libraries.
6. run_tests.py now reports all missing and extra files. The logic for
   finding these has been reworked.