* merge RCommand and RScript into single launcher RMain
* add script install_r_native_image that builds FastR with native-image tool
and updates the bash launchers

(cherry picked from commit f29e18bc)

- Make sure there is no suite loading ordering issues by avoiding the
capture of suites at module-loading time.
- Make sure the SULONG build-time dependency is only added to
`r.native.recommended` if the project is available (i.e., fastr is not a
binary suite)

* Replace `FastRNativeRecommendedProject` hack with a build dependency
* Replace most of `FastRArchiveParticipant` with a build dependency

Refactor ffi impls into com.oracle.truffle.r.ffi.impl project; add ffi AP; TruffleLLVM all RFFI interfaces implemented; no JNI

Started to implement S4 dispatch.