[regression] Handle deprecated KibanaThemeProvider uses to include Ki… · pmuellr/kibana@f2b07fc

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[regression] Handle deprecated KibanaThemeProvider uses to include Ki…

…banaRenderContextProvider (elastic#163103)

## Summary

Unfortunately, elastic#161914 regressed elastic#162365 in that many plugins and their
Emotion styles (including EUI emotion styles) are now missing a cache
and are being appended to to the end of the document `<head>` as opposed
to within `<meta name="emotion">`.

What appears to be happening is many plugins are using a parent
`<KibanaThemeProvider>` but **not** a parent
`<KibanaRootContextProvider>` (not sure if this work is TBD or in
progress). This means that a parent `<EuiProvider>`, (which determines
the cache insertion of child Emotion styled components) is missing,
which is causing several CSS specificity bugs, e.g. around datagrid.

As a somewhat-bandaid-y fix, I've bogarted EUI's nested provider context
to check if the theme provider has a parent `EuiProvider`, and if it
doesn't, to use `KibanaEuiProvider` instead of `KibanaThemeProvider`.
This should set up the caches and context if needed, or otherwise simply
use the original `KibanaThemeProvider` component.

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Co-authored-by: kibanamachine <[email protected]>
Co-authored-by: Clint Andrew Hall <[email protected]>