FCP 7 XML: Time Remaps result in incorrect OTIO Frame range

This github issue is capturing info from a slack thread: https://academysoftwarefdn.slack.com/archives/CMQ9J4BQC/p1605578837228200

### Incorrect Functionality and General Questions

The original TC information is properly contained in xml, but TC is expressed differently in OTIO View. This seems to be caused by a Time Remap.

## To Reproduce

See attached example files: [fcp_xml.tar.gz](https://github.com/PixarAnimationStudios/OpenTimelineIO/files/5907584/fcp_xml.tar.gz)

There is a retime in the 2nd clip of the 1st track.
The values we want are StartTC = 10:25:02:15, EndTC(exclusive) = 10:25:06:15, Duration: 96.997.
But in the current OTIO, the result of modifying the code so that we do not change the 24fps to 23.978 even with the NTSC option is StartTC = 10:24:59:02, EndTC (exclusive) = 10:25:01:02, Duration: 48 (don’t changed)
also, the result of activating the NTSC Option is: StartTC = 10:24:21:15, EndTC (exclusive) = 10:24:23:15, Duration: 48 (don’t changed)
In addition, it is the same timeline, but it is not recognized by fcpxml. (Because of the NTSC option, 23.976fps -> 23fps is changed.)

Unpack the attached fcp_xml.tar.gz and reproduce the retime in the second clip of the first track through the FCP 7 XML import path. Compare the imported OTIO time range with the stated StartTC, exclusive EndTC, and duration, both with and without the NTSC option; done means the remapped clip reports the intended values without changing its duration.

Written by the indexing model from the issue text.