Add resizable virtual display feature

Introduce `--flex-display` to continuously resize the virtual display
to match the window.

app/data/bash-completion/scrcpy

@@ -108,7 +108,8 @@ _scrcpy() {
         --window-x=
         --window-y=
         --window-width=
-        --window-height="
+        --window-height=
+        -x --flex-display"
 
     _init_completion -s || return
 

app/data/zsh-completion/_scrcpy

@@ -113,6 +113,7 @@ arguments=(
     '--window-y=[Set the initial window vertical position]'
     '--window-width=[Set the initial window width]'
     '--window-height=[Set the initial window height]'
+    {-x,--flex-display}'[Continuously resize the virtual display to match the window]'
 )
 
 _arguments -s $arguments