feat: add content field in TextAnchor (#294)

* feat: add `content` field in TextAnchor

PiperOrigin-RevId: 435142243

Source-Link: googleapis/googleapis@721b367

Source-Link: googleapis/googleapis-gen@b627aae
Copy-Tag: eyJwIjoiLmdpdGh1Yi8uT3dsQm90LnlhbWwiLCJoIjoiYjYyN2FhZWIzYWZhZmU3ZDk0ZDYwOTlhMmQxOTQ1YWE5YjRkYWRhZCJ9

* 🦉 Updates from OwlBot post-processor

See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md

Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>

packages/google-cloud-documentai/google/cloud/documentai_v1beta2/types/document.py

@@ -673,6 +673,9 @@ class TextAnchor(proto.Message):
             text_segments (Sequence[google.cloud.documentai_v1beta2.types.Document.TextAnchor.TextSegment]):
                 The text segments from the
                 [Document.text][google.cloud.documentai.v1beta2.Document.text].
+            content (str):
+                Contains the content of the text span so that users do not
+                have to look it up in the text_segments.
         """
 
         class TextSegment(proto.Message):
@@ -699,6 +702,7 @@ class TextSegment(proto.Message):
         text_segments = proto.RepeatedField(
             proto.MESSAGE, number=1, message="Document.TextAnchor.TextSegment",
         )
+        content = proto.Field(proto.STRING, number=2,)
 
     class PageAnchor(proto.Message):
         r"""Referencing elements in