Add function to paste from clipboard and add support for non-US locales

[chschnell]

To paste text from the system clipboard into the emulator support for international keyboard layout mappings is needed for non-US users (in text mode, support for non-US codepages is additionally needed). This problem is laid out in detail in issue #1406.

User interface changes

• added "Locale" setting to emulator setup (us, uk, de, default: us), each locale defines a codepage and a keyboard layout mapping
• added "Send clipboard" function button to paste current system clipboard content into the emulator (can be aborted by pressing Esc)

API changes

• removed delay argument from V86.keyboard_send_scancodes() and V86.keyboard_send_text(), not needed any more (moved to KeyboardAdapter config)
• removed V86.keyboard_send_keys(codes, delay), this isn't supported any more (deprecated and wasn't used in the source tree anyway)
• added V86.keyboard_send_keypress(keys, hold_time) as a replacement, keys is an array of strings in KeyboardEvent.code naming convention
• added V86 configuration option options.locale to set the Locale at startup (default: us)

Changes to class KeyboardAdapter

• split implementation into separate DesktopKeyboard and DataKeyboard classes
• DesktopKeyboard handles interactive keyboard input from the system keyboard in desktop browser environments
• DataKeyboard handles all other cases in which we feed an arbitrary large amount of data into the keyboard pipeline programatically, which can be a unicode string, a synthetic key-press event or a sequence of raw scancodes
• for consistency, DesktopKeyboard is muted whenever DataKeyboard is feeding scancodes into the keyboard pipeline
• removed dependencies on deprecated KeyboardEvent.keyCode (as much as possible, help needed)
• removed charmap[] and asciimap[]
• added KEYMAPS[], maps unicode characters to scancode combinations for selected keyboard layouts
• moved away from using raw scancode numbers in the source tree in favour of string-typed key names from the KeyboardEvent.code naming convention

Demos

Use case 1: Pasting all extended German keys into nano (Debian 12 German in text console mode):

debian-de-paste-keyboard-kbdgr.mp4

Use case 2: Mobile screenshot FreeDOS 1.4 German:

Use case 3: German keyboard layout mapping and copdepage in vga2tty with FreeDOS 1.4 German:

See vga2tty.

freedos14-de-vga2tty-kbdgr.mp4

TODO

• tooling: keyboard layout mappings are currently generated by an external python script, this could be moved to ./tools/ in the source tree. The same is true for the generation of codepage mappings. Both scripts need a bit of work and discussion before though.
• CapsLock: the CapsLock state of the system keyboard is currently ignored (the key itself is handled correctly, but its active/inactive state is not handled), haven't really looked into this yet
• internal mapping objects for codepages, keyboard layouts and locales are currently scattered across lib.js, browser/keyboard.js and browser/starter.js (respectively), maybe these should be at the same place because they are related, but where?