FastR Grid: LPolygon + support for 'stringwidth' units

...com/oracle/truffle/r/library/fastrGrid/DoSetViewPort.java

...com/oracle/truffle/r/library/fastrGrid/GridLinesNode.java

.../com/oracle/truffle/r/library/fastrGrid/GridTextNode.java

...src/com/oracle/truffle/r/library/fastrGrid/GridUtils.java

...y/src/com/oracle/truffle/r/library/fastrGrid/LCircle.java

.../src/com/oracle/truffle/r/library/fastrGrid/LConvert.java

...ry/src/com/oracle/truffle/r/library/fastrGrid/LLines.java

...y/src/com/oracle/truffle/r/library/fastrGrid/LPoints.java

.../src/com/oracle/truffle/r/library/fastrGrid/LPolygon.java

...ary/src/com/oracle/truffle/r/library/fastrGrid/LRect.java

...src/com/oracle/truffle/r/library/fastrGrid/LSegments.java

...rary/src/com/oracle/truffle/r/library/fastrGrid/Unit.java

.../nodes/builtin/base/foreign/CallAndExternalFunctions.java

mx.fastr/copyrights/overrides