respect invisible text attribute

This is a weird attribute TBH.

xterm seems to replace the cells with spaces: copying and pasting
results in spaces.

Kitty ignores it.

VTE doesn't render it but allows copying and pasting.

The latter is now also the behavior in wezterm.

docs/changelog.md

@@ -37,6 +37,7 @@ As features stabilize some brief notes about them will accumulate here.
   [#2491](https://github.com/wez/wezterm/pull/2492)
 * Panic when processing a sixel with inconsistent width information
   [#2500](https://github.com/wez/wezterm/issues/2500)
+* Cells with the invisible/hidden attribute are now invisible
 
 ### 20220905-102802-7d4b8249
 

wezterm-gui/src/termwindow/render.rs

@@ -2990,7 +2990,7 @@ impl super::TermWindow {
                                 pane: params.pane,
                             });
 
-                            if glyph_color == bg_color {
+                            if glyph_color == bg_color || cluster.attrs.invisible() {
                                 // Essentially invisible: don't render it, as anti-aliasing
                                 // can cause a ghostly outline of the invisible glyph to appear.
                                 continue;