Add support for local instance posts

A new platform feature is defined, `@akkoma/local-only`, which is marked as present only if the string `akkoma` is found in the instance version string.

If this feature is supported, a new post visibility option is added to the post compose visibility selector, "Local instance", which sets the visibility to `"local"`.

The post viewer is also updated accordingly; while local-only posts could already be seen previously, they didn't have anything written in the `.extra-meta` section, and didn't display a visibility icon.

The `building` icon has been selected as the symbol for "Local instance" posts, as it's already used in the main menu to denote the Local timeline.

src/components/compose.jsx

@@ -1178,6 +1178,11 @@ function Compose({
                 <option value="direct">
                   <Trans>Private mention</Trans>
                 </option>
+                {supports('@akkoma/local-only') &&
+                  <option value="local">
+			        <Trans>Local instance</Trans>
+		          </option>
+                }
               </select>
             </label>{' '}
           </div>

src/components/status.jsx

@@ -94,6 +94,7 @@ const visibilityText = {
   unlisted: msg`Unlisted`,
   private: msg`Followers only`,
   direct: msg`Private mention`,
+  local: msg`Local instance`,
 };
 
 const isIOS =

src/utils/supports.js

@@ -7,6 +7,8 @@ import { getCurrentInstance } from './store-utils';
 // Non-semver(?) UA string detection
 const containPixelfed = /pixelfed/i;
 const notContainPixelfed = /^(?!.*pixelfed).*$/i;
+const containAkkoma = /akkoma/i
+const notContainAkkoma = /^(?! *akkoma) *$/i
 const platformFeatures = {
   '@mastodon/lists': notContainPixelfed,
   '@mastodon/filters': notContainPixelfed,
@@ -20,6 +22,7 @@ const platformFeatures = {
   '@pixelfed/trending': containPixelfed,
   '@pixelfed/home-include-reblogs': containPixelfed,
   '@pixelfed/global-feed': containPixelfed,
+  '@akkoma/local-only': containAkkoma,
 };
 const supportsCache = {};
 

src/utils/visibility-icons-map.js

@@ -3,4 +3,5 @@ export default {
   unlisted: 'group',
   private: 'lock',
   direct: 'message',
+  local: 'building',
 };