StoreGate: Add ReadDecorHandle::withDefault.

Add withDefault() method to ReadDecorHandle. This works like operator(), except that one specifies a default value to return if the variable is not available. This allows removing some instances of isAvailable().

Build area was cleaned as per request posted in the DB. The full software build will be performed

This merge request affects 1 package:

• Control/StoreGate

This merge request affects 3 files:

• Control/StoreGate/StoreGate/ReadDecorHandle.h
• Control/StoreGate/StoreGate/ReadDecorHandle.icc
• Control/StoreGate/test/ReadDecorHandle_test.cxx

Adding @ssnyder as watcher

added Core main review-pending-level-1 labels

CI Result SUCCESS (hash f326275f)

	Athena	AthSimulation	AthGeneration	AthAnalysis
externals
cmake
make
tests

Full details available on this CI monitor view. Check the JIRA CI status board for known problems
Athena: number of compilation errors 0, warnings 0
AthSimulation: number of compilation errors 0, warnings 0
AthGeneration: number of compilation errors 0, warnings 0
AthAnalysis: number of compilation errors 0, warnings 0
For experts only: Jenkins output [CI-MERGE-REQUEST-EL9 9381] (remote access info)

MR looks fine from L1 perspective, CI shows no problems - approving

Cheers, Qiyu, L1

removed review-pending-level-1 label

added review-approved label

merged

mentioned in commit 82c48709