* [Docs] [Icons] Updating dart doc styles to recognize more styles of icons. All the 4 icon styles we support have to be pulled from 4 individual web fonts when we show the html page for api docs.
* Better documentation and that special awful case.
* Couple more places to remove.
This PR modifies the existing API docs samples to use DartPad so that all of the samples are now interactive apps on the API docs site.
It also removes the restriction for the max width of the description area so that the dartpad region can expand horizontally.
I updated the first paragraph on the API docs to indicate that Flutter is more than just mobile now (same text as the README.md at the top level).
I modified a few of the examples so that they looked nicer, and fit better on the page.
I added the sample description text above each DartPad instance, since that often defines the context of the example.
I removed animations and images when they were redundant with the sample content. There were a few that made sense to keep, so I did.
When converting all of the samples to use the snippet tool, I encountered some bugs/shortcomings:
1. The document production took 90 minutes, since the snippet tool was being invoked from the command line each time. I fixed this by snapshotting the executable before running, so it's down to 7 minutes.
2. The sample code was not being properly escaped by the snippet tool, so generics were causing issues in the HTML output. It is now quoted.
3. Code examples that used languages other than Dart were not supported. Anything that highlight.js was compiled for dartdoc with is now supported.
4. The comment color for highlight.js was light grey on white, which was pretty unreadable. It's now dark green and bold.
This creates a custom dartdoc tool that will generate snippet blocks in our API docs that allow the user to copy easily to the clipboard, and will also embed the snippet code into a template to show it in a larger context with an app.
This PR adds the snippet tool, a template, and a couple of HTML skeleton files, one for snippets that are designed to be in an application setting, and one where it simply puts a nice container around existing snippets, making them easier to copy to the clipboard.
