Make SNSPowderReduction work with various splitter workspaces

[wdzhou]

Make SNSPowderReduction work with various types of workspaces that contain splitters.

To test:

a1. create 1 splitters workspaces by GenerateEventsFilter. Set 'FastLog' to True. The splitter workspace should be a MatrixWorkspace
a2. run SNSPowderReduction with this MatrixWorkspace splitters.

b1. create a 3 column TableWorkspace. column 0 and 1 should be float, and column should be string. Column 0 should be the start time of a splitter; column 1 be the stop time; and column 3 be the target workspace tag.
b2. run SNSPowderReduction with this TableWorkspace.

Fixes #19139.

New feature is reported in the release note.

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[peterfpeterson]

I tried out the PD interface and the system tests that aren't usually run. Everything works.