Add a private template that provides in-place reverse for an array.
The algorithm works from the middle of the array, working outwards and
swapping elements between the front and the back.  It can only be used
for types that are suitable for use with `std::swap()`; either
trivially copyable, or with an implementation of `T::swap(T& other)`.

Add a function that reverses a mutable list instance in place.

Add a function that reverses the order of bytes in a mutable `MCData`
instance in-place.

Strings cannot be reversed in-place in the general case.  There is no
upper limit on the number of codeunits in a grapheme, which means that
a temporary buffer of at the same length of the string is required for
general correctness.

This patch adds a "reversed copy" function which performs a deep copy
of the source string, and then constructs the reversed form in the
copy by re-reading from the source string via a grapheme break
iterator.

In practice, the "trivial" flag is not getting set for trivial
strings, so all strings that use UTF-16 internal representatino go
through the slow grapheme break iterator path.

Add the ability to reverse a binary string in an LCB program with a
new `reverse tData` statement.

Add the ability to reverse the order of bytes in a list with the
`reverse tList` statement.

Add a new function to reverse an LCB string in-place using the
`reverse tString` statement.

Now that there is a `reverse` statement, provide an alternative
example of looping over the contents of a string.