Administration: Fix Dashicon backwards compatibility issues.

In [44940], the Dashicon files in core were updated to contain the latest version of the font from the GitHub repo. This change follows that up by fixing several backwards compatibility issues caused by the new build process used to generate the font files and fixes the missing menu icon when viewing the admin on small screens.

- `buddicons-bbpress-logo (f12b)` was moved back to the correct location of `f477`.
- `editor-ltr (f129)` was moved back to the correct location of `f10c`.
- `email-alt2 (f10a)` was moved to the correct location of `f467`. 

The following icons were restored to their previous locations:

- `camera-alt (f129)`
- `edit-large (f327)`
- `editor-distractionfree (f211)`
- `update-alt (f113)`
- `twitter-alt (f302)`
- `text-page (f121)`
- `plugins-checked (f485)`
- `menu-alt3 (f349)`
- `menu-alt2 (f329)`
- `menu-alt (f228)`
- Duplicate lock icon at location `f315`
- Duplicate `editor-code` icon at location `f494`
- `arrow-up` at `f143`.

The `editor-ltr` and `editor-rtl` icons had also been switched. The arrows now point in the correct directions at the correct Unicode locations (`f10c` and `f320` respectively).

And, lastly, this change also introduces the `code-standards (f13a)` icon that was not included in the previous build.

Props afercia, earnjam, oztaser, joen, cathibosco1, ianbelanger, desrosj.
See #41074.
Fixes #46611.

git-svn-id: https://develop.svn.wordpress.org/trunk@45040 602fd350-edb4-49c9-b593-d223f7449a82

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