add local caching interface in MagneticField

[slava77]

This issue is to address the performance scaling problem resulting from cache trashing of the cache used in the MagGeometry (internal to the VolumeBasedMagneticField) observed in multi-threaded applications.
As a follow up to #28180, in line with #28180 (comment), an update to the interface is expected in 2019 with follow up PR(s) to enable/benefit from local caching.

For convenience, a copy from #28180 (comment)
it will be straightforward to move the internal cache up to MagGeometry::fieldInTesla(const GlobalPoint& gp) and add a separate MagGeometry::fieldInTesla(const GlobalPoint& gp, MagneticFieldCache& cache) since these are very simple methods.

@namapane @amadio @dpiparo

[cmsbuild]

A new Issue was created by @slava77 Slava Krutelyov.

@davidlange6, @Dr15Jones, @smuzaffar, @fabiocos, @kpedro88 can you please review it and eventually sign/assign? Thanks.

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[slava77]

assign reconstruction,simulation

[cmsbuild]

New categories assigned: reconstruction,simulation

@mdhildreth,@slava77,@perrotta,@civanch you have been requested to review this Pull request/Issue and eventually sign? Thanks

[civanch]

@slava77 , @namapane , @amadio, how will proceed? who will make PR(s)?

[namapane]

@civanch, as I mentioned in #28180 I can add the new interface but I am working on other developments in the same subsystem that I'd prefer to finish beforehand. It will take a couple of weeks I hope. Otherwise it's fine for me if that is done independently by somebody else; just let me know.

[namapane]

This should be probably closed with #29561 .

[slava77]

+1

via discussion related to #29561