fix(frontend): Improve paste handler for table cells

This replaces the broken approach from #3906.

* Only regard paste handler if pasting to a table cell (Fixes: #4443)
* Add all (marked) text nodes with newlines in between
* Only add a newline for non-text nodes to prevent newlines in between
  text with changing marks.

Signed-off-by: Jonas <jonas@freesources.org>

Author: mejo-

src/nodes/Table/TableCell.js

@@ -37,27 +37,27 @@ export default TableCell.extend({
 		return [
 			new Plugin({
 				props: {
-					// Special-treat empty lines in pasted content to prevent jumping out of cell
+					// Only paste (marked) text into table cells to prevent jumping out of cell
 					handlePaste: (view, event, slice) => {
-						if (slice.content.childCount > 1) {
-							const state = view.state
-							const childCount = slice.content.childCount
-							const childNodes = []
-							for (let i = 0; i < childCount; i++) {
-								if (i === 0) {
-									childNodes.push(state.schema.text('\n'))
-								}
-
-								// Ignore empty children (i.e. empty lines)
-								if (!slice.content.child(i).firstChild) {
-									continue
-								}
+						if (!this.editor.isActive(this.type.name)) {
+							return false
+						}
 
-								childNodes.push(state.schema.text(slice.content.child(i).textContent, slice.content.child(i).firstChild.marks))
+						const { state } = view
+						const childNodes = []
+						let newLineAdded = false
+						slice.content.descendants((node, pos) => {
+							if (node.isText) {
+								childNodes.push(state.schema.text(node.textContent, node.marks))
+								newLineAdded = false
+							} else if (!newLineAdded) {
+								childNodes.push(state.schema.text('\n'))
+								newLineAdded = true
 							}
-							const newNode = view.state.schema.node('paragraph', [], childNodes)
-							slice.content = Fragment.empty.addToStart(newNode)
-						}
+						})
+
+						const newNode = state.schema.node('paragraph', [], childNodes)
+						slice.content = Fragment.empty.addToStart(newNode)
 					},
 				},
 			}),