PLT-5747: Fixed inconsistent on-hover, tooltip, and active states for buttons. (#7174)

* Fixed LHS Team Sidebar on hover highlight.
 * Fixed LHS Main Menu on hover tooltip to show "Main menu".
 * Added On-hover highlight for Favorite button in channel heading.
 * Added active state for channel members icon.
   * Added active class based on internal react state with new changeCss rule.
 * Changed cursor to pointer on hovering a theme.
 * Fixed Invite New Member Add Button to have text-underline on hover.

webapp/i18n/en.json

@@ -2155,6 +2155,7 @@
   "shortcuts.browser.highlight_next": "Highlight text to the next line:\tShift|Down",
   "shortcuts.browser.newline": "Create a new line:\tShift|Enter",
   "sidebar.channels": "PUBLIC CHANNELS",
+  "sidebar.mainMenu": "Main Menu",
   "sidebar.createChannel": "Create new public channel",
   "sidebar.createGroup": "Create new private channel",
   "sidebar.direct": "DIRECT MESSAGES",