fix: parse $t() nesting options block that spans multiple lines (#2440)

The options-vs-formatters boundary in nest() detected the options
object with /{.*}/, whose dot does not match line breaks. A nesting
options block containing a newline was therefore treated as having no
options, so the whole block was mis-split as trailing formatters and
the interpolation variables inside it were dropped. Match across line
breaks with the dotAll flag.