Fix T78084: Search does not accept text fragments everywhere

This was reported for the "Add Node" search functionality, but is
relevant in other searches as well.

So e.g. when searching for "Separate XYZ", typing "sep", then " " (with
the intention to type "X" next) would clear the search field. Now use
the same method (matching against all search words) as in F3 searching
('menu_search_update_fn') in other searches as well [searching IDs,
property objects, finding nodes,...]

This should give a much nicer search experience in general.

Note: this does not touch other searches in the Dopesheet, Outliner,
Filebrowser or User Preferences that have other search implementations.

Maniphest Tasks: T78084

Differential Revision: https://developer.blender.org/D8232

source/blender/blenlib/tests/BLI_string_test.cc

@@ -570,6 +570,16 @@ TEST(string, StringStrncasestr)
   EXPECT_EQ(res, (void *)NULL);
 }
 
+/* BLI_string_max_possible_word_count */
+TEST(string, StringMaxPossibleWordCount)
+{
+  EXPECT_EQ(BLI_string_max_possible_word_count(0), 1);
+  EXPECT_EQ(BLI_string_max_possible_word_count(1), 1);
+  EXPECT_EQ(BLI_string_max_possible_word_count(2), 2);
+  EXPECT_EQ(BLI_string_max_possible_word_count(3), 2);
+  EXPECT_EQ(BLI_string_max_possible_word_count(10), 6);
+}
+
 /* BLI_string_is_decimal */
 TEST(string, StrIsDecimal)
 {