RFR(m): 8177290 add copy factory methods for unmodifiable List, Set, Map

[Stephen Colebourne]

On 19 November 2017 at 03:34, John Rose <john.r.rose at oracle.com> wrote:
> Meanwhile, `toUnmodifiableList` is so ugly to the ear,
> eye, and fingers that it will be less used just because of
> its long spelling.

Many developers are already using Google Guava which has added
toImmutableList() and friends. More widely, we use the toXxx() form
for all the collectors we've written (in OpenGamma Strata). As such, I
think the toXxx() naming is well established at this point, and
toUnmodifiableList() will be fine.

Stephen