Adds a flag to CastBaseNode that indicates that it should behave in a way
compatible with coercions exposed by the R native interface.

"testthat" has been tested running tests of package "argparse".

- implemented RFFI functions PRSEEN, PRENV, R_PromiseExpr, and PRCODE
- cleanup of method "getIntrinsicValue"; replaced by RASTUtils.createLanguageElement
- added dummy cast to node IsATTY
- also fixed FileConnections.writeString; was required to run a package
- added tests for R exception handling; since we still have bugs, some tests are ignored
- also fixed a problem during source code parsing in REngine, which occurred if the code contained empty lines that have not been suppressed by any shell

rffi; replace UpCallsIndex with RFFIUpCallMethod enum; fix bug in R_NewHashedEnv signature; simplify RForeignAccessFactoryImpl

Adapted to changes in GR-1767: frame parameter removed from interop functions and transitively from all callers where possible.
Also updated Truffle version in file "suite.py".
Removed class TruffleRFFIFrameHelper since there are no usages any longer.
Removed unnecessary call to CompilerDirectives.transferToInterpreter call in class ValuePrinterNode.

RFFI: refactor upcalls into separate interfaces; fix R_Home/R_Interactive rewrites; make tempdir context sensitive, clean up CallRFFI