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.

Implemented TruffleRLanguage.toString(RContext context, Object value) and isVisible() to work properly in GraalVM shell and Interop.

coalesce all seq builtins into SeqFunctions
add fast paths for seq and seq.default
refactor and expand seq unit tests

- code corresponding to 'nmath' in GnuR moved to new package:
com.oracle.truffle.r.runtime.nmath
- it turns that Wilcox uses Choose, which is a builtin node, the original
structure did not allow code reuse in such cases
- implement wilcox externals {d/p/q}wilcox and wilcox_free + improved choose

Externals implemented: {p/q/d/r}nbinom, and {p/q/d}nbinom_mu

- use RMathError
- fix format String in debugging messages
- move methods from GammaFunctions to RMath
- fix javadoc in QuantileSearch

getCanonicalFile() removes any '..' from the path. Some IDEs (intellij) put
'..' into StandardLocation.SOURCE_OUTPUT. With '..' the getParentFile() does
not work as intended.

+ small fix in RErrorHandling: when max number of warnings is reached, do not
report the actual number, but the max (like GnuR does).

Provide parameter values for each distribution separately +
honor semantics of common parameters like probability in [0,1] etc.

Few minor fixes of bugs discovered along the way.

Plus 'pgamma' external implemented.

+ necessary DPQ/RMath methods
+ move all XChisq to Chisq.java