dartdoc: top-levels should be after interfaces, classes, and exceptions

[DartBot]

This issue was originally filed by @seaneagan

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Top-level methods, getters, setters, and variables are currently at the beginning of the output. They may contain extensive comments. This pushes the links to interfaces, classes, and exceptions "after the fold" and thus makes them much more difficult to find. Some good examples are:

http://api.dartlang.org/uri.html
http://api.dartlang.org/dart_isolate.html

Moving the top-levels to the end would fix this.

[iposva-google]

Added Area-DartDoc, Accepted labels.

[munificent]

Most libraries have more classes than top-level functions, so I'd hate to always push them under that potentially long list. Maybe we could do:

1. List of top-level definitions without docs. Each has an anchor link to 3.
2. List of types, which link to type pages.
3. Top-level definitions with their docs.

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   Added this to the Later milestone.

[dgrove]

to fix in the next generation dartdoc viewer.

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cc @jmesserly.
cc @sigmundch.
Set owner to @jacob314.

[DartBot]

This comment was originally written by amouravski@google.com

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Marked this as being blocked by #8857.

[jacob314]

Set owner to @efortuna.

[efortuna]

cc @alan-knight.
Removed the owner.

[alan-knight]

Removed Area-DartDoc label.
Added Area-DartDocNext label.

[alan-knight]

Libraries vary in what's most important to expose. I think the reasonable answer to this is to have good navigation. So, in the current Dartdoc-next http://dartdoc-next.dartlang-api.appspot.com/apidocs/ we still have functions first in a library, but there's a navigation bar on the right in which you can easily scroll down to see the classes. And you can collapse the list of functions, or classes, if they're not interesting. So calling this fixed.

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Added Fixed label.