chore(bigtable): Rerouted legacy client row filters to data client row filters (#18175)

Migrating over @gkevinzheng PR from bigtable monorepo
googleapis/python-bigtable#1255

### Original description:
> Changes made:
> - Used import aliasing to remove most of the legacy client row filter
code and use the data client row filter code in its place.
> - Some of the data client row filter classes had to be slightly
modified for backwards compatibility with the legacy client row filter
classes' interface.
> - As part of this move, `to_pb` has been replaced with `_to_pb`, and I
have adjusted references to `<RowFilter>.to_pb` in the libraries and
unit tests.
> 
> This is for eventually shimming up `CheckAndMutateRows`, and other row
mutation operations as well.


### Additional changes on top of Kevin's:
-
([3097276](3097276))
I added an alias between the new `_to_pb()` and the old `to_pb()`
methods, for backwards compatibility
- Originally, we were planning on dropping the method. Now, it can still
be used, with a deprecation warning

Note to reviewers: This PR has already been reviewed and merged to a
staging branch, with the intention of doing a single merge to main. We
are now planning to slowly rollout these changes back to the main
branch. Minimal re-review should be necessary

---------

Co-authored-by: Kevin Zheng <147537668+gkevinzheng@users.noreply.github.com>

Author: daniel-sanche

packages/google-cloud-bigtable/google/cloud/bigtable/row.py

@@ -231,7 +231,7 @@ def _delete_cells(self, column_family_id, columns, time_range=None, state=None):
         else:
             delete_kwargs = {}
             if time_range is not None:
-                delete_kwargs["time_range"] = time_range.to_pb()
+                delete_kwargs["time_range"] = time_range._to_pb()
 
             to_append = []
             for column in columns:
@@ -602,7 +602,7 @@ def commit(self):
         resp = data_client.check_and_mutate_row(
             table_name=self._table.name,
             row_key=self._row_key,
-            predicate_filter=self._filter.to_pb(),
+            predicate_filter=self._filter._to_pb(),
             app_profile_id=self._table._app_profile_id,
             true_mutations=true_mutations,
             false_mutations=false_mutations,