fix(text area): set attributes before calling _set_document

Ensure `TextArea.__init__()` assigns attributes like
`soft_wrap` *before* calling the `_set_document()` method.

Currently if you create a `TextArea` with `soft_wrap=False`, the
document is first wrapped with the default `soft_wrap=True`, causing an
initial flicker.

Author: TomJGooding

src/textual/widgets/_text_area.py

@@ -500,6 +500,11 @@ def __init__(
         self._cursor_offset = (0, 0)
         """The virtual offset of the cursor (not screen-space offset)."""
 
+        self.set_reactive(TextArea.soft_wrap, soft_wrap)
+        self.set_reactive(TextArea.read_only, read_only)
+        self.set_reactive(TextArea.show_line_numbers, show_line_numbers)
+        self.set_reactive(TextArea.line_number_start, line_number_start)
+
         self._set_document(text, language)
 
         self.language = language
@@ -510,11 +515,6 @@ def __init__(
         reactive is set as a string, the watcher will update this attribute to the
         corresponding `TextAreaTheme` object."""
 
-        self.set_reactive(TextArea.soft_wrap, soft_wrap)
-        self.set_reactive(TextArea.read_only, read_only)
-        self.set_reactive(TextArea.show_line_numbers, show_line_numbers)
-        self.set_reactive(TextArea.line_number_start, line_number_start)
-
         self.tab_behavior = tab_behavior
 
         if tooltip is not None: