Cleaned up implementations of integer, double, string and logical casts, as well as implementations of the respective conversion builtins. Introduced new tests and enabled additional ones fixed by previous modifications.

Fixes to vector casts and attributes printing. Enabled tests fixed by the previously introduced changes.

Vectors should be made shared when required by the use of the copy and not at the point of making the copy itself.

Implemented the non-replacement form of the "dimnames" function, enabled the replacement form, and added tests.

FastR: an implementation of R in Java atop Truffle and Graal. Contributed by Tomas Kalibera, Petr Maj, and Jan Vitek (Purdue University); Christian Humer and Andreas Woess (Johannes Kepler University Linz); Michael Haupt, Mick Jordan, Adam Welc, Christian Wirth, and Thomas Wuerthinger (Oracle Labs).