Support osc 52 Manipulate Selection Data. #343

[jixiuf]

this pull request need merged after #404

Add option: vterm-enable-manipulate-selection-data-by-osc52

Vterm support copy text to emacs kill ring and system clipboard by using OSC 52.
See https://invisible-island.net/xterm/ctlseqs/ctlseqs.html for more info about OSC 52.
For example: send 'blabla' to kill ring(and clipboard): printf "\033]52;c;$(printf "%s" "blabla" | base64)\a"

tmux can share its copy buffer to terminals bysupporting osc52(like iterm2 xterm),
you can enable this feature for tmux by :
set -g set-clipboard on #osc 52 copy paste share with iterm
set -ga terminal-overrides ',xterm*:XT:Ms=\E]52;%p1%s;%p2%s\007'
set -ga terminal-overrides ',screen*:XT:Ms=\E]52;%p1%s;%p2%s\007'

The clipboard querying/clearing functionality offered by OSC 52 is not implemented here,

And for security reason, this feature is disabled by default."

This feature need the new way of handling strings with a struct VTermStringFragment
in libvterm. You'd better compile emacs-libvterm with cmake -DUSE_SYSTEM_LIBVTERM=no ...
If you don't do that, when the content you want to copied is too long, it would be truncated
by bug of libvterm.