build: xterm 6.0.0 for the serial console

@xterm/xterm 6.0.0 and @xterm/addon-fit 0.11.0 replace xterm 3.6.0; the page reads typed and pasted input with onData, and no longer writes every key and all terminal output to the browser console. The unused fullscreen addon goes.

static/css/xterm.css

@@ -36,8 +36,7 @@
  */
 
 .xterm {
-    font-family: courier-new, courier, monospace;
-    font-feature-settings: "liga" 0;
+    cursor: text;
     position: relative;
     user-select: none;
     -ms-user-select: none;
@@ -56,21 +55,21 @@
      * The z-index of the helpers must be higher than the canvases in order for
      * IMEs to appear on top.
      */
-    z-index: 10;
+    z-index: 5;
 }
 
 .xterm .xterm-helper-textarea {
-    /*
-     * HACK: to fix IE's blinking cursor
-     * Move textarea out of the screen to the far left, so that the cursor is not visible.
-     */
+    padding: 0;
+    border: 0;
+    margin: 0;
+    /* Move textarea out of the screen to the far left, so that the cursor is not visible */
     position: absolute;
     opacity: 0;
     left: -9999em;
     top: 0;
     width: 0;
     height: 0;
-    z-index: -10;
+    z-index: -5;
     /** Prevent wrapping so the IME appears against the textarea at the correct position */
     white-space: nowrap;
     overflow: hidden;
@@ -113,10 +112,6 @@
     top: 0;
 }
 
-.xterm .xterm-scroll-area {
-    visibility: hidden;
-}
-
 .xterm-char-measure-element {
     display: inline-block;
     visibility: hidden;
@@ -126,33 +121,46 @@
     line-height: normal;
 }
 
-.xterm {
-    cursor: text;
-}
-
 .xterm.enable-mouse-events {
     /* When mouse events are enabled (eg. tmux), revert to the standard pointer cursor */
     cursor: default;
 }
 
-.xterm.xterm-cursor-pointer {
+.xterm.xterm-cursor-pointer,
+.xterm .xterm-cursor-pointer {
     cursor: pointer;
 }
 
-.xterm.xterm-cursor-crosshair {
+.xterm.column-select.focus {
     /* Column selection mode */
     cursor: crosshair;
 }
 
-.xterm .xterm-accessibility,
+.xterm .xterm-accessibility:not(.debug),
 .xterm .xterm-message {
     position: absolute;
     left: 0;
     top: 0;
     bottom: 0;
     right: 0;
-    z-index: 100;
+    z-index: 10;
     color: transparent;
+    pointer-events: none;
+}
+
+.xterm .xterm-accessibility-tree:not(.debug) *::selection {
+  color: transparent;
+}
+
+.xterm .xterm-accessibility-tree {
+  font-family: monospace;
+  user-select: text;
+  white-space: pre;
+}
+
+.xterm .xterm-accessibility-tree > div {
+  transform-origin: left;
+  width: fit-content;
 }
 
 .xterm .live-region {
@@ -162,3 +170,116 @@
     height: 1px;
     overflow: hidden;
 }
+
+.xterm-dim {
+    /* Dim should not apply to background, so the opacity of the foreground color is applied
+     * explicitly in the generated class and reset to 1 here */
+    opacity: 1 !important;
+}
+
+.xterm-underline-1 { text-decoration: underline; }
+.xterm-underline-2 { text-decoration: double underline; }
+.xterm-underline-3 { text-decoration: wavy underline; }
+.xterm-underline-4 { text-decoration: dotted underline; }
+.xterm-underline-5 { text-decoration: dashed underline; }
+
+.xterm-overline {
+    text-decoration: overline;
+}
+
+.xterm-overline.xterm-underline-1 { text-decoration: overline underline; }
+.xterm-overline.xterm-underline-2 { text-decoration: overline double underline; }
+.xterm-overline.xterm-underline-3 { text-decoration: overline wavy underline; }
+.xterm-overline.xterm-underline-4 { text-decoration: overline dotted underline; }
+.xterm-overline.xterm-underline-5 { text-decoration: overline dashed underline; }
+
+.xterm-strikethrough {
+    text-decoration: line-through;
+}
+
+.xterm-screen .xterm-decoration-container .xterm-decoration {
+	z-index: 6;
+	position: absolute;
+}
+
+.xterm-screen .xterm-decoration-container .xterm-decoration.xterm-decoration-top-layer {
+	z-index: 7;
+}
+
+.xterm-decoration-overview-ruler {
+    z-index: 8;
+    position: absolute;
+    top: 0;
+    right: 0;
+    pointer-events: none;
+}
+
+.xterm-decoration-top {
+    z-index: 2;
+    position: relative;
+}
+
+
+
+/* Derived from vs/base/browser/ui/scrollbar/media/scrollbar.css */
+
+/* xterm.js customization: Override xterm's cursor style */
+.xterm .xterm-scrollable-element > .scrollbar {
+    cursor: default;
+}
+
+/* Arrows */
+.xterm .xterm-scrollable-element > .scrollbar > .scra {
+	cursor: pointer;
+	font-size: 11px !important;
+}
+
+.xterm .xterm-scrollable-element > .visible {
+	opacity: 1;
+
+	/* Background rule added for IE9 - to allow clicks on dom node */
+	background:rgba(0,0,0,0);
+
+	transition: opacity 100ms linear;
+	/* In front of peek view */
+	z-index: 11;
+}
+.xterm .xterm-scrollable-element > .invisible {
+	opacity: 0;
+	pointer-events: none;
+}
+.xterm .xterm-scrollable-element > .invisible.fade {
+	transition: opacity 800ms linear;
+}
+
+/* Scrollable Content Inset Shadow */
+.xterm .xterm-scrollable-element > .shadow {
+	position: absolute;
+	display: none;
+}
+.xterm .xterm-scrollable-element > .shadow.top {
+	display: block;
+	top: 0;
+	left: 3px;
+	height: 3px;
+	width: 100%;
+	box-shadow: var(--vscode-scrollbar-shadow, #000) 0 6px 6px -6px inset;
+}
+.xterm .xterm-scrollable-element > .shadow.left {
+	display: block;
+	top: 3px;
+	left: 0;
+	height: 100%;
+	width: 3px;
+	box-shadow: var(--vscode-scrollbar-shadow, #000) 6px 0 6px -6px inset;
+}
+.xterm .xterm-scrollable-element > .shadow.top-left-corner {
+	display: block;
+	top: 0;
+	left: 0;
+	height: 3px;
+	width: 3px;
+}
+.xterm .xterm-scrollable-element > .shadow.top.left {
+	box-shadow: var(--vscode-scrollbar-shadow, #000) 6px 0 6px -6px inset;
+}