Make SVG related functions public and add their documentation

.../truffle/r/library/fastrGrid/FastRGridExternalLookup.java

.../oracle/truffle/r/library/fastrGrid/device/SVGDevice.java

...ruffle/r/library/fastrGrid/grDevices/R/fastrGridDevices.R

...om/oracle/truffle/r/library/fastrGrid/grDevices/Rd/awt.Rd

...racle/truffle/r/library/fastrGrid/grDevices/Rd/svg.off.Rd

...le/truffle/r/library/fastrGrid/grDevices/Rd/svg.string.Rd

...acle/truffle/r/library/fastrGrid/grDevices/SvgString.java

.../com/oracle/truffle/r/nodes/builtin/base/BasePackage.java

...om/oracle/truffle/r/nodes/builtin/base/R/base_overrides.R

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

...c/com/oracle/truffle/r/nodes/builtin/fastr/FastRHelp.java

.../oracle/truffle/r/nodes/builtin/utils/R/utils_overrides.R

.../com/oracle/truffle/r/test/library/fastr/TestInterop.java

...src/com/oracle/truffle/r/test/library/utils/TestHelp.java