This might not be the best rework - I was unsure if the *this* that would be available when called would see the appropriate object so I assumed not and pass it as a parameter.
Works, but may be bad form.
Original handling of snippets only worked if the current selected theme was a staticTheme. This now fully merges all snippets through the theme chain no matter what the top-level theme is. So user themes built on 5ePHB can benefit from 5ePHB snippets too.
User input of user snippets will be a later PR, but merging them into static snippets is now supported.
Themes contain both CSS and Snippets. The brewRenderer only cares about the CSS, but other components need the Snippets. Better to have the parent "editPage", etc. load the theme bundles and pass them down to each child that needs it, rather than trying to pass from the child up.
This also fixes the `metadataEditor.jsx` not being able to change themes live; A new theme bundle is now loaded when a new theme is selected, instead of only the first time the BrewRenderer mounts.
Also renamed to "fetchThemeBundle"
`renderStyle` is still necessary; it allows us to update the style live in the component render step as the user types into the style tab. Otherwise the style is only rendered once and never updates.
React also discourages directly editing the DOM ourselves, because it makes changes to the DOM that react cannot track; we should aim to provide all DOM writes inside of the component render function instead of using `document.createElement`, etc.
Too that end, this commit reduces the `loadAllStylesAndSnippets` function to just fetch and parse the data; actual rendering is moved back to `renderStyle()`
Each theme in the theme chain, including user brews, must use the same renderer. When moving to V4 or future versions, it will be important to distinguish which themes are compatible with each other
Since /edit and /new endpoints now have an `await` inside that could return an error (`getUsersBrewThemes()`), asyncHandler must be added to pass errors along instead of just crashing
