[BE] Use CamelCase for enum class members (#79772)
Per many C++ code-style guides members(for [example](https://google.github.io/styleguide/cppguide.html#Enumerator_Names) ) members of `enum` should be CamelCased,
and only defines should be ALL_CAPS
Changes `MemOverlap`, `MemOverlapStatus` and `CmpEvalResult` enum values
Also, `YES`, `NO`, `TRUE` and `FALSE` are often system defines
Fixes among other things, current iOS build regression, see, which manifests as follows (see [this](https://hud.pytorch.org/pytorch/pytorch/commit/6e90572bb9443266e1abe5c7d737b028926d9b6b):
```
/Users/runner/work/pytorch/pytorch/aten/src/ATen/MemoryOverlap.h:19:29: error: expected identifier
enum class MemOverlap { NO, YES, TOO_HARD };
^
/Applications/Xcode_12.4.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator14.4.sdk/usr/include/objc/objc.h:89:13: note: expanded from macro 'YES'
#define YES __objc_yes
```
Pull Request resolved: https://github.com/pytorch/pytorch/pull/79772
Approved by: https://github.com/drisspg, https://github.com/kulinseth
