The `:` char is used as a metadata marker in `$localize` messages.
If this char appears in the metadata it must be escaped, as `\:`.
Previously, although the `:` char was being escaped, the TS AST
being generated was not correct and so it was being output double
escaped, which meant that it appeared in the rendered message.
As of TS 3.6.2 the "raw" string can be specified when creating tagged
template AST nodes, so it is possible to correct this.
PR Close#33820
Pete Bacon Darwin
Filipe Silva