refactoring: rename CallNode -> RCallNode (preparation for adoption of Truffle changes around CallNode handling)

adopt inlining changes suggested by Christian Humer (preparation for adopting changes around CallNode handling)

mx_fastr: add gate check for AllTests/FailingTests in sync; fix bug in --gen-diff; use 'with VM' for bench

tell the one-shot GNU R session used in tests to be friendly to FastR's current level of support for source attribution, and enable one test that passes

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.