Implement MFC-style source locator compression (#2212)

* Implement MFC-style source locator compression

* Fix formatting issues

* Fix emitting empty FileInfo if the firrtl doesn't have one

* Remove '.scala' requirement in FileInfo parsing regex

* Handle parsing of FileInfos with no line/col nums

* Split FileInfos only if they match

This should fix any issues with FileInfos that do not use the "file line:col"
format, and allow any valid firrtl using these info comments to compile.

* Add unit tests for locator compression

* Move InfoTests to InfoSpec class

* Fix existing unit tests with fileinfo comments

* Add unit tests to ignore the algorithm's own output