Make Log.jsm functions support tagged template literals. For example,
instead of |logger.debug("foo " + bar)| or |logger.debug(`foo ${bar}`)|,
you can now use |logger.debug `foo ${bar}`| (without parentheses).
Using tagged template literals has the benefit of less verbosity
compared to regular string concatenation, with the added benefit of
lazily-stringified parameters -- the parameters are only stringified
when logging is enabled, possibly saving from an expensive stringify
operation.
This patch also fixes a bug in BasicFormatter where consecutive tokens
are not formatted correctly (e.g. "${a}${b}").
MozReview-Commit-ID: 9kjLvpZF5ch
128ab3a796