Rename of getThreadIndex to getIndex

[mondus]

Fixes #898 .

Simple fix by renaming. Not used in any tests only internally in a few places. Testing of this seems like overkill.

Addition of getIndex to host API can be dealt with as a separate enhancement issue as it is already achievable using iterator logic.

[ptheywood]

This does not close the referenced issue, which is explicilty for a getIndex method which is for both the hsot and device components, although it is part of that issue (and the most immediately required one.

Could you edit the PR description and remove the Fixes statement so it doens't auto close the issue? We can move it in the prioritisaiton board when this is done.

[mondus]

This does not close the referenced issue, which is explicilty for a getIndex method which is for both the hsot and device components, although it is part of that issue (and the most immediately required one.

Could you edit the PR description and remove the Fixes statement so it doens't auto close the issue? We can move it in the prioritisaiton board when this is done.

@ptheywood I've just added the host version of this instead along with a test for host side which is less trivial than the device API.

[ptheywood]

Added a python test for AgentVector for you, but not for DeviceAgentVector as there isn't a test file for that yet (see #557).

Otherwise looks good to (squash) merge (subject to CI)