* Finish moving things into test/backend

* Update CODEOWNERS for moved file

* Tweak GPU manifest for renamed test

* [MLIR] Fix naming convention in MLIR files

Add naming convention note per file to state which files should use
nGraph naming convention and which MLIR naming convention and align
naming convention in those files with such a note.

* Remove m-prefix

[CMAKE] Change CODEGEN error on windows to be more grammatically correct

Leona/doc v0.24

[MLIR] Enable Gather Op

Add nbench support for double buffering

Remove support for adjoints of nodes

Python capsules support for ngraph::Function

* Pad: add pad mode SYMMETRIC

* Style.

* Disable UT on unsupported backends.

* Make required numpy version explicit.

* Read setup requirements from requirements.txt

Restore DEFAULT_FLOAT_TOLERANCE_BITS logic in lrn, sigmoid, softmax. Should allow re-enabling PlaidML tests (#3277)

* Added rpath setting for PlaidML backend

* Fix colons

* Separate build and install rpath

* Explicitly set target properties