Set embedded app theme to match the site theme

[sfc-gh-dmatthews]

📚 Context

This PR passed the currently selected theme to all Community Cloud embedded apps as a query parameter to make them match the site theme.

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[sfc-gh-tteixeira]

Approved after comments addressed

[sfc-gh-tteixeira]

Why is the function needed?

[sfc-gh-tteixeira]

If currentTheme isn't used anywhere else, I think it's cleaner to just instantiate it to "dark_theme" or "light_theme" directly, rather than do a more brittle string interpolation later on.

[sfc-gh-tteixeira]

Actually, just instantiate to embed_options=dark_theme directly, and avoid a second string interpolation below.

Same for light.

[sfc-gh-tteixeira]

It's cleaner to add the theme directly in the embedQueryParams array, and let the string joining logic above handle it.

That is, remove the if (query) { block but keep the code inside, modified like this:

    const embedQueryParams = [themeParam];
    const normalQueryParams = [];

    if (query) {
      query.split("&").forEach((qStr) => {
        if (qStr.startsWith("embed=") || qStr.startsWith("embed_options=")) {
          embedQueryParams.push(qStr);
        } else {
          normalQueryParams.push(qStr);
        }
      });
    }

    embedQueryStr = "&" + embedQueryParams.join("&");
    normalQueryStr = "&" + normalQueryParams.join("&");

[sfc-gh-dmatthews]

I think I followed your suggestions. I couldn't get rid of the function entirely, because server-side rendering broke. So, re-requested a review to make sure it satisfies you requests.

[sfc-gh-dmatthews]

Actually, the breaks a portion. Apps from docstrings only load in light mode. I'll update it again.

[sfc-gh-dmatthews]

I changed it to use a theme context to so that API pages would load with the correct theme. The first fix had the following problem:

1. Load in light theme
2. Switch to dark theme
3. Navigate to API page
4. Apps were light, but could toggle to light and back to dark to make them dark

The new fix will load the right them for the API apps, even if the theme was changed sometime after the first load.