[Tools>Board] and [Sketch>Include Library] split ridiculous long menus into sub-menus

The **Tools > Board** menu is very long. Scrolling in this menu is not convenient and seems to have (had) many bugs.

Indeed the Boards already are grouped by "Arduino AVR-Boards" etc.
These groups could/should simply be transformed to a submenu.

Thus boards are simpler and quicker to reach and scroll'n'search is reduced largely.
Also since list of boards is getting longer every day the current menu is not future proof.

Same may happen with the **Sketch > Include Library** menu. There also a grouping is existing and could be used.
Libraries not fitting into the three groups could get an own submenu.

I have only ESP32, ESP8266 and Micro/Mini/MegaCore Boardmanagers and even on FHD+ screen the menu is 3x longer as the screen. Scrolling really takes some time and simply the wrong solution to this problem.

Related to all versions up to 1.8.9 on Windows and afaik also on Linux.

Start by locating the menu construction for Tools > Board and Sketch > Include Library in the Arduino IDE. Review how board and library groups are currently represented, then verify that the groups become submenus and that long lists no longer require excessive scrolling.

Written by the indexing model from the issue text.