AthContainers: Some updates to DataVector.

Some updates to DataVector, to be more consistent with recent standards.

• Declare some methods noexcept, where possible. (Some methods that are noexcept in std::vector do in fact throw exceptions with DataVector.)
• Declare empty as [[nodiscard]] as well as noexcept
• Have emplace_back return the pointer being pushed. For DataVector, we do the same thing for push_back,

The CI job for this MR was stuck due to build machine problem. Restarting.

Jenkins please retry a build

WARNING: big files (>100K) are found in the changeset

112K in file Control/AthContainers/AthContainers/DataVector.icc

140K in file Control/AthContainers/test/DataVector_test.icc

112K in file Control/AthContainers/AthContainers/DataVector.h

This merge request affects 1 package:

• Control/AthContainers

Adding @ssnyder as watcher

added Core master review-pending-level-1 labels

CI Result FAILURE (hash cffe2c37)

	Athena	AthSimulation	AthGeneration	AnalysisBase
externals
cmake
make
required tests
optional tests

Full details available on this CI monitor view
Athena: number of compilation errors 0, warnings 0
AthSimulation: number of compilation errors 0, warnings 0
AthGeneration: number of compilation errors 0, warnings 0
AnalysisBase: number of compilation errors 0, warnings 0
For experts only: Jenkins output [CI-MERGE-REQUEST-CC7 19056]

CI failure known and unrelated. Approving (L2 shifter)

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

merged

mentioned in commit 42639537

added sweep:ignore label