Refactor common quantile search code from QPois and QBinom + tests

...library/src/com/oracle/truffle/r/library/stats/QPois.java

...ibrary/src/com/oracle/truffle/r/library/stats/Qbinom.java

...rc/com/oracle/truffle/r/library/stats/QuantileSearch.java

...library/src/com/oracle/truffle/r/library/stats/RMath.java

...ibrary/src/com/oracle/truffle/r/library/stats/Wilcox.java

...acle/truffle/r/nodes/builtin/base/BaseGammaFunctions.java

...est/src/com/oracle/truffle/r/test/ExpectedTestOutput.test

...racle/truffle/r/test/library/stats/TestDistributions.java

...racle/truffle/r/test/library/stats/TestStatFunctions.java

mx.fastr/copyrights/overrides