common : implement common_schema internal representation for JSON schemas (#28736)

* common : implement common_schema types

* common : implement a json schema optimizer

* common : reduce optimizations

* common : refactor json-schema-to-grammar to use common_schema

* common : use common_trie

* common/schema : implement type/kind resolution

* cont : cleanup

* cont : remove common_chat_tool_parameters

* cont : simplify schema resolution

* cont : pass common_schema through the json-schema-to-grammar builder

* cont : cleanup

* cont : move enums under common_schema and add type enum

* cont : reduce test cases

* cont : clean up

* cont : clean up

* refactor : rename common_schema_parse to common_schema_from_json

* tests : fix gcc dangling-reference warning in test-json-schema

* tests : take the schema label as const char * to satisfy gcc dangling-reference

* refactor : rename common_schema_builder parse_* methods to build_*

* cont : fix may_be_string

* cont : properly handle empty tool parameters

* cont : add tests for empty $ref

* cont : remove dead code

* cont : update docs

* cont : make "{}" mean any object for json_object as well

* cont : restore (min|max)Length to imply string type

* cont : rename common_schema to common_chat_schema

tests/test-grammar-integration.cpp

@@ -918,7 +918,7 @@ static void test_json_schema() {
     // Otherwise, this test structure is the same.
 
     test_schema(
-        "empty schema (object)",
+        "empty schema (any value)",
         // Schema
         R"""(
             {}
@@ -927,14 +927,16 @@ static void test_json_schema() {
         {
             R"""({})""",
             R"""({"foo": "bar"})""",
-        },
-        // Failing strings
-        {
-            "",
             "[]",
             "null",
             R"""("")""",
             "true",
+        },
+        // Failing strings
+        {
+            "",
+            R"""({"foo"})""",
+            "foo",
         }
     );