Add altClickForMouseEvents option for issue #5952

When enabled during mouse events mode, click/drag/move events require the alt
key while wheel events are unaffected. Selection stays enabled by default
and takes precedence over macOptionClickForcesSelection.

Co-authored-by: Daniel Imms <Tyriar@users.noreply.github.com>

typings/xterm-headless.d.ts

@@ -38,6 +38,16 @@ declare module '@xterm/headless' {
      */
     altClickMovesCursor?: boolean;
 
+    /**
+     * When enabled and the terminal is in mouse events mode, mouse click, drag,
+     * and move events are only sent to the underlying application when the alt
+     * key is held. Wheel events are not affected. This allows normal text
+     * selection by default while still supporting application mouse interaction
+     * and scrolling when holding alt. When enabled, this takes precedence over
+     * `macOptionClickForcesSelection`.
+     */
+    altClickForMouseEvents?: boolean;
+
     /**
      * When enabled the cursor will be set to the beginning of the next line
      * with every new line. This is equivalent to sending '\r\n' for each '\n'.

typings/xterm.d.ts

@@ -45,6 +45,16 @@ declare module '@xterm/xterm' {
      */
     altClickMovesCursor?: boolean;
 
+    /**
+     * When enabled and the terminal is in mouse events mode, mouse click, drag,
+     * and move events are only sent to the underlying application when the alt
+     * key is held. Wheel events are not affected. This allows normal text
+     * selection by default while still supporting application mouse interaction
+     * and scrolling when holding alt. When enabled, this takes precedence over
+     * `macOptionClickForcesSelection`.
+     */
+    altClickForMouseEvents?: boolean;
+
     /**
      * When enabled the cursor will be set to the beginning of the next line
      * with every new line. This is equivalent to sending `\r\n` for each `\n`.