Change description of privacy levels to be more intuitive in web UI (#13197)

* Improve description of privacy levels in compose interface

* Change strings in defaultMessage and source as well as english

Co-authored-by: Thibaut Girka <thib@sitedethib.com>

app/javascript/mastodon/locales/defaultMessages.json

@@ -1073,7 +1073,7 @@
         "id": "privacy.public.short"
       },
       {
-        "defaultMessage": "Post to public timelines",
+        "defaultMessage": "Visible for all, shown in public timelines",
         "id": "privacy.public.long"
       },
       {
@@ -1081,7 +1081,7 @@
         "id": "privacy.unlisted.short"
       },
       {
-        "defaultMessage": "Do not show in public timelines",
+        "defaultMessage": "Visible for all, but not in public timelines",
         "id": "privacy.unlisted.long"
       },
       {
@@ -1089,7 +1089,7 @@
         "id": "privacy.private.short"
       },
       {
-        "defaultMessage": "Post to followers only",
+        "defaultMessage": "Visible for followers only",
         "id": "privacy.private.long"
       },
       {
@@ -1097,7 +1097,7 @@
         "id": "privacy.direct.short"
       },
       {
-        "defaultMessage": "Post to mentioned users only",
+        "defaultMessage": "Visible for mentioned users only",
         "id": "privacy.direct.long"
       },
       {

app/javascript/mastodon/locales/en.json

@@ -319,13 +319,13 @@
   "poll_button.add_poll": "Add a poll",
   "poll_button.remove_poll": "Remove poll",
   "privacy.change": "Adjust status privacy",
-  "privacy.direct.long": "Post to mentioned users only",
+  "privacy.direct.long": "Visible for mentioned users only",
   "privacy.direct.short": "Direct",
-  "privacy.private.long": "Post to followers only",
+  "privacy.private.long": "Visible for followers only",
   "privacy.private.short": "Followers-only",
-  "privacy.public.long": "Post to public timelines",
+  "privacy.public.long": "Visible for all, shown in public timelines",
   "privacy.public.short": "Public",
-  "privacy.unlisted.long": "Do not post to public timelines",
+  "privacy.unlisted.long": "Visible for all, but not in public timelines",
   "privacy.unlisted.short": "Unlisted",
   "refresh": "Refresh",
   "regeneration_indicator.label": "Loading…",