cherry-pick PATInterfaces package from 21.2

Pretty straight-forward cherry-pick, plus adding the package to AnalysisBase.

Turns out the main difference were updates to copyrights, but some code changes were done as well.

List of commits involved:

• a64076b3 Fixing the package's build in standalone mode with CMake (PATInterfaces-00-00-35)
• afec45c1 Updated to PATInterfaces-00-00-38.
• c410de54 added test for SystematicSet clearing
• 9b309e93 Fixed SystematicSet clear behavior.
• a580600d boost::unordered_map --> std::unordered_map : ROOT-8890
• 54078d0b replace ISU copyright with CERN copyright
• ffdb051f make sure an empty string translates to an empty SystematicSet

changed the description

This merge request affects 2 packages:

• PhysicsAnalysis/AnalysisCommon/PATInterfaces
• Projects/AnalysisBase

Adding @krumnack ,@akraszna ,@rbianchi as watchers

added Analysis Build master review-pending-level-1 labels

Not sure if the CI is running behind the scenes, I guess yes, an annoying feature certainly...

Looks good in general, just waiting for the CI to finish

removed review-pending-level-1 label

resolved all threads

added review-pending-level-1 label

CI Result SUCCESS (hash 1774a7b0)

	Athena	AthSimulation	AnalysisBase	AthGeneration
externals
cmake
make
required tests
optional tests

Full details available on this CI monitor view
Athena: number of compilation errors 0, warnings 1
AthSimulation: number of compilation errors 0, warnings 0
AnalysisBase: number of compilation errors 0, warnings 0
AthGeneration: number of compilation errors 0, warnings 0
For experts only: Jenkins output [CI-MERGE-REQUEST-CC7 12285]

Warning is unrelated to the changes in this MR.

Looks good, approving --L1

added review-approved label and removed review-pending-level-1 label

mentioned in commit b5139f85

merged

added sweep:ignore label