Remove lodash merge

[AndrewMusgrave]

WHY are these changes introduced?

Part of removing lodash #991

WHAT is this pull request doing?

Creating a less featureful merge function and using that instead of _.merge

How to 🎩

Test pass? 💯

TODO:

• add changelog

[BPScott]

Repeating my query from #1010 here too:

I'm not too familiar with how mergeAppProviderOptions() and legacy context stuff does its thing, but do we need a deep merge there and in the withAppProvider / withSticky HoCs or could we get away with a shallow one using Object.assign()?

[AndrewMusgrave]

Unfortunately merging context requires a deep merge since the user could define partial context and have it collide with polaris.

[solonaarmstrong-zz]

Elegant! 👌

[AndrewMusgrave]

Ready for 👀

[dleroux]

I rebased it because conflicts with Michelle's autobind.

[dleroux]

I assume we skip change logs for these?

[dleroux]

Although I wonder why percy changed. It's not being translated?

[AndrewMusgrave]

I assume we skip change logs for these?

Iv'e been adding them to Code Quality 😄