Add error calculation to FlipperEfficiency algorithm

[rbauststfc]

Description of work

Summary of work

Calculates the errors using the equation given on the linked issue. This is required because default Mantid error calculation is not sufficiently accurate when applying polarisation corrections.

Fixes #37458

Further detail of work

This change should be a direct implementation of the equation on the linked issue. The only exception is that the equation shown includes the modulus symbol around the square of the partial derivatives, which I haven't included in the implementation. My understanding is that because the values are being squared it won't make a difference here, but please let me know if this is not correct.

To test:

Can be tested with the following script:

CreateSampleWorkspace(OutputWorkspace='out_00', Function='User Defined', UserDefinedFunction='name=Lorentzian, Amplitude=48000, PeakCentre=2.65, FWHM=1.2', XUnit='wavelength', NumBanks=1, BankPixelWidth=1, XMin=0, XMax=16.5, BinWidth=0.1)
CreateSampleWorkspace(OutputWorkspace='out_11', Function='User Defined', UserDefinedFunction='name=Lorentzian, Amplitude=47000, PeakCentre=2.65, FWHM=1.2', XUnit='wavelength', NumBanks=1, BankPixelWidth=1, XMin=0, XMax=16.5, BinWidth=0.1)
CreateSampleWorkspace(OutputWorkspace='out_10', Function='User Defined', UserDefinedFunction='name=Lorentzian, Amplitude=22685, PeakCentre=2.55, FWHM=0.6', XUnit='wavelength', NumBanks=1, BankPixelWidth=1, XMin=0, XMax=16.5, BinWidth=0.1)
CreateSampleWorkspace(OutputWorkspace='out_01', Function='User Defined', UserDefinedFunction='name=Lorentzian, Amplitude=22685, PeakCentre=2.55, FWHM=0.6', XUnit='wavelength', NumBanks=1, BankPixelWidth=1, XMin=0, XMax=16.5, BinWidth=0.1)

group = GroupWorkspaces(['out_00','out_11','out_10','out_01'])

group = ConvertUnits(group, "Wavelength")

out = FlipperEfficiency(group, SpinStates="00, 11, 10, 01")

# Should give result approximately equal to 0.024600439254069618
print(out.readE(0)[0])

To check the documentation changes, build the docs-html target.

This does not require release notes because it is a change to an algorithm that is new in version 6.10.

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[jclarkeSTFC]

Partial derivatives agree with Wolfram Alpha, algorithm runs as expected. The errors are now much smaller than they were previously (ZOOM 22708), as expected: