Update to clang-format-5 and reformat the codebase 

Refs #22197

Refs #22197

- No validation of dx for histograms

Refs #22197

Refs #22197

Refs #22197

Refs #22197

Refs #22197

Refs #22197

Refs #22197

Refs #22197

- and precise release notes
- and add a draft usage example

Refs #22197

Refs #22197

- added test to compare if input workspaces get modified when running Stitch1D. Unfortunately this is the case for point and binned data.

Refs #22197

Refs #22197

Refs #22197

- new method scaleWorkspace which reinserts Dx values for point data
- deleted MantidDataObjects/WorkspaceSingleValue.h from Multiply and Divide
- introduced new class variables m_scaleFactor and m_errorScaleFactor; those values will now be initialised by 1.0 (the default value) and not 0.0 as before.
- deleted unused tool-tip texts (Optional.)
- ConjoinXRuns output workspace property is a Workspace and not a MatrixWorkspace -> dynamic pointer cast
- unit tests for histograms pass
- MantidPlot executes for point data example from unit test
- unit test for point data fails (SortXAxis, Python algorithm, not registered!)

Refs #22197

Refs #22197

Refs #22197

- update release notes

Refs #22197

Refs #22197

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Refs #22197

This uses the -fix option on clang-tidy to automatically fix all
the unused usings declarations that have crept into Mantid.