TextSource* API update (#1255)

* Add collapse function to TextSource*

* Add isConnected getter to TextSource*

ext/fg/js/text-source-element.js

@@ -40,6 +40,10 @@ class TextSourceElement {
         return this._endOffset;
     }
 
+    get isConnected() {
+        return this._element.isConnected;
+    }
+
     clone() {
         return new TextSourceElement(this._element, this._fullContent, this._startOffset, this._endOffset);
     }
@@ -73,6 +77,15 @@ class TextSourceElement {
         return delta;
     }
 
+    collapse(toStart) {
+        if (toStart) {
+            this._endOffset = this._startOffset;
+        } else {
+            this._startOffset = this._endOffset;
+        }
+        this._content = '';
+    }
+
     getRect() {
         return this._element.getBoundingClientRect();
     }

ext/fg/js/text-source-range.js

@@ -41,6 +41,13 @@ class TextSourceRange {
         return this._imposterSourceElement;
     }
 
+    get isConnected() {
+        return (
+            this._range.startContainer.isConnected &&
+            this._range.endContainer.isConnected
+        );
+    }
+
     clone() {
         return new TextSourceRange(this._range.cloneRange(), this._content, this._imposterContainer, this._imposterSourceElement);
     }
@@ -74,6 +81,11 @@ class TextSourceRange {
         return length - state.remainder;
     }
 
+    collapse(toStart) {
+        this._range.collapse(toStart);
+        this._content = '';
+    }
+
     getRect() {
         return this._range.getBoundingClientRect();
     }