Turn ISIS SANS compatibility mode off by default

[rbauststfc]

Description of work

Summary of work

The compatibility mode feature in the ISIS SANS GUI was intended to be temporary, but this wasn't revisited as intended and the feature is currently being applied by default to all SANS reductions. When reducing event data, this is causing some very small differences in the results at the extreme ranges of the q range, which is not desirable. For now it is sufficient to simply turn this feature off by default. In a future release we will look at removing it entirely.

Fixes #38053

To test:

1. Go to Interfaces->SANS->ISIS SANS.
2. Go to the Settings tab (from the left side of the window).
3. The Use compatibility mode checkbox should not be selected, but should be enabled (so you should still be able to select it, if desired).

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[GuiMacielPereira]

Checked that option of compatibility mode is disabled by default. Code is straight forward and looks good.