TrigKernel: Further clean-up and make it a header-only library

Further clean-up of the TrigKernel package following up from !29024 (merged):

• Remove HltExtraStatusCode - although it has been possibly recorded in some Run-2 data, it has never been used and it seems no decoding of these codes has ever been implemented in Athena
• Remove HltOnlHelper which was only serving the purpose of enum->string mapping
• Implement much cleaner way of enum->string mapping for the remaining enum PSCErrorCode
• Adapt clients to the above change
• Thanks to the above, it was now possible to make TrigKernel a header-only library

This merge request affects 3 packages:

• HLT/Event/TrigByteStreamCnvSvc
• HLT/Trigger/TrigControl/TrigKernel
• HLT/Trigger/TrigControl/TrigServices

Adding @wiedenma ,@bernius ,@fwinkl ,@rbielski as watchers

added Trigger master review-pending-level-1 labels

CI Result FAILURE

	Athena	AthSimulation
externals
cmake	N/A	N/A
make	N/A	N/A
required tests	N/A	N/A
optional tests	N/A	N/A

Due to problems in externals build or cmake configuration the job is stopped, results are not available on the ATLAS CI monitor For experts only: Jenkins output [CI-MERGE-REQUEST-CC7 7470]

Same error as other MRs. Let's wait until this is fixed before restarting.

Jenkins please retry a build

This merge request affects 3 packages:

• HLT/Event/TrigByteStreamCnvSvc
• HLT/Trigger/TrigControl/TrigKernel
• HLT/Trigger/TrigControl/TrigServices

Adding @wiedenma ,@bernius ,@fwinkl ,@rbielski as watchers

CI Result SUCCESS (hash b85cc000)

	Athena	AthSimulation
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
For experts only: Jenkins output [CI-MERGE-REQUEST-CC7 7521]

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

merged

mentioned in commit a45bc810

added sweep:ignore label