wrap QMatrix in namespace pcl to resolve linker conflict with Qt6

[maz-1]

fixes conflict with QtGui. Resolves #4857

[larshg]

Need to fix format to clang style, see here for required changes https://dev.azure.com/PointCloudLibrary/pcl/_build/results?buildId=19641&view=logs&jobId=84ba2080-ade3-55e3-f209-94ce73f9d406&j=84ba2080-ade3-55e3-f209-94ce73f9d406&t=9838d42f-a715-5615-242f-7e73bf03078b

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[mvieth]

Thank you!

[kunaltyagi]

Probably also wrap the Kernel class 😆

[jspricke]

@kunaltyagi Why is this flagged ABI break?
As far I can see this is an internal class.
Note that we can't have ABI breaks in patch releases as they don't bump the Soname, so either this should not have been in 1.12.1 or this is not an ABI break?

[kunaltyagi]

Yeah, I also thought there would be no ABI break, however, the tooling used (.github/generate_abi_reports.sh) verified the following:

• change of namespace affected symbol names and signatures internal to the library, but the symbols are visible outside as well

This would not have resulted in ill-formed programs post linkage.

since this is a cpp file, the chances of someone actually relying on this are minimal and would require the person to be personally compiling PCL. Hence the decision to flag as ABI break for those people, but still send it in a minor release

[mvieth]

Here is the full report for the ml module:
compat_report_ml_1.12.1.zip