new ChannelAccess client library

[shroffk]

Incorporate https://github.com/channelaccess/ca as a datasource in Phoebus / eclipse CS-Studio

[kasemir]

Summary of discussion:

Channel access is the proven, stable, legacy protocol with jca/caj as the original Java implementation.
We continue to support Channel Access via bugfixes and minor adjustments like making hardcoded settings configurable, but there is no plan to fundamentally extend jca/caj nor to change to a different implementation.
Any development effort for additions or improvements would be devoted to PV Access.