Handle spaces in multiple file property

[samtygier-stfc]

Description of work

DO NOT MERGE yet, still has debugging code

This changes the regular expression used to separate groups of filenames to be more robust against spaces after commas.

It results in POLARIS146554, 146603-146609, 146616 being treated the same as POLARIS146554,146603-146609,146616. This is a change from the current behaviour which would treat it as POLARIS146554, XXX146603-146609, XXX146616 where XXX is the current default instrument.

The previous regex used to find the commas that separate groups of files from separate instruments:
NUM_COMMA_ALPHA(R"((?<=\d)\s*,\s*(?=\D))")
uses a lookahead with \D to find a comma followed by something that did not start with a digit. E.g. this would match the comma in ,ALF123 but not ,123. The bug is that it also matches , 123 because the space is a non-digit character. Because we now have a group with a filename that starts with a number, the default instrument is assumed.

This fix replaces \D with [a-zA-Z] so that a new group is only started if there is a new instrument name.

Related to #40648
Closes #40793

To test:

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[samtygier-stfc]

There are a few test failures. This will need to handle cases like:
LagrangeILLReduction(SampleRuns="014412.nxs, 014412_scan_continues.nxs")