Text log scroll end (#2127)

* added switches

* snapshot

* changelog

* tweak docstrings

* Update src/textual/widgets/_text_log.py

Co-authored-by: Rodrigo Girão Serrão <5621605+rodrigogiraoserrao@users.noreply.github.com>

---------

Co-authored-by: Rodrigo Girão Serrão <5621605+rodrigogiraoserrao@users.noreply.github.com>

tests/snapshot_tests/snapshot_apps/textlog_scroll.py

@@ -0,0 +1,35 @@
+from textual.app import App, ComposeResult
+from textual.widgets import TextLog
+from textual.containers import Horizontal
+
+
+class TextLogScrollApp(App):
+    CSS = """
+    TextLog{
+        width: 1fr;
+        height: 10;
+    }
+    """
+
+    def compose(self) -> ComposeResult:
+        with Horizontal():
+            # Don't scroll on write
+            yield TextLog(id="textlog1", auto_scroll=False)
+            # Scroll on write
+            yield TextLog(id="textlog2", auto_scroll=True)
+            # Scroll on write, but disabled on write()
+            yield TextLog(id="textlog3", auto_scroll=True)
+
+    def on_ready(self) -> None:
+        lines = [f"Line {n}" for n in range(20)]
+        for line in lines:
+            self.query_one("#textlog1", TextLog).write(line)
+        for line in lines:
+            self.query_one("#textlog2", TextLog).write(line)
+        for line in lines:
+            self.query_one("#textlog3", TextLog).write(line, scroll_end=False)
+
+
+if __name__ == "__main__":
+    app = TextLogScrollApp()
+    app.run()