[GR-6936] Cache for installed packages for package test infrastructure.

...oracle/truffle/r/engine/shell/EmbeddedConsoleHandler.java

...oracle/truffle/r/ffi/impl/common/JavaUpCallsRFFIImpl.java

...pl/src/com/oracle/truffle/r/ffi/impl/nodes/MiscNodes.java

...com/oracle/truffle/r/ffi/impl/upcalls/StdUpCallsRFFI.java

.../com/oracle/truffle/r/launcher/DefaultConsoleHandler.java

....launcher/src/com/oracle/truffle/r/launcher/RCommand.java

...y/src/com/oracle/truffle/r/library/utils/OctSizeNode.java

...oracle.truffle.r.native/fficall/src/common/rffi_upcalls.h

...e.truffle.r.native/fficall/src/common/rffi_upcallsindex.h

...racle.truffle.r.native/fficall/src/truffle_common/Utils.c

com.oracle.truffle.r.native/version.source

...in/src/com/oracle/truffle/r/nodes/builtin/base/Order.java

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

.../com/oracle/truffle/r/nodes/unary/SizeToOctalRawNode.java

com.oracle.truffle.r.test.packages/r/install.packages.R

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

...com/oracle/truffle/r/test/builtins/TestBuiltin_order.java

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

...rc/com/oracle/truffle/r/test/library/utils/TestUtils.java

documentation/dev/pkgtest.md