1. modify set_value op, use Scalars to represent attr `values`, instead of a bunch of attributs of various types; (#52408)

2. add program converter and set_value op as an example, which provides the functionality to convert `paddle::framework::ProgramDesc` between old and new formats(the differences are mainly some operators with incompatible updates in the definition);
3. program version and operator version map now are always saved when serializing `paddle::framework::ProgramDesc` to identify the version;
3. provide an option `legacy_format=false` in  serialization of `paddle::framework::ProgramDesc`, it decided whether to convert ProgramDesc back to a legacy format, which is compatible for paddle 2.4.2 or earlier versions to load and execute;
4. deserialization of `paddle::framework::ProgramDesc` is now automatically detecting whether the bytes it receives is in legacy format(contains any of the operators that has been incompatibly updated and have any attribute of type `Scalar`) and convert it to new format. But if you want a faithful deserialization without the automatic conversion, you can use protobuf's deserialization instead. Though it is not recommended, it can be used for the purpose of testing.

Add basic functionalities to support Scalar & Scalars in operator attribute.

1. extend allowed types in operator's attribute type, add `paddle::experimental::Scalar`, add corresponding protobuf Message types;
2. Scalar enhancement, add formatting, equality;
3. add code to handle Scalar & Scalars in opmaker, conversion from  paddle operator to phi kernel, opdesc construction and manipulation,  tensorrt converter, tracer, operator construction, etc;
4. bind `paddle::experimental::Scalar` to python, as `libpaddle.Scalar`;
5. add functionality to canonicalize attribute map according to OpProto(if the op the attribute map used for has an OpProto);
6. add code to manipulate Scalar proto message via protobuffer python API;

Add unittests.

1. add test cases for formatting, equality for Scalars, and WrapAsScalars;
2. add test cases for 'casting' between different morphs of attributes;
3. add test cases for extracting scalar & scalars from attribute;
4. add test cases for CanonicalizeScalarAttrs(and fix a bug in type index offset);
5. fix gmock's library filename on windows platform.
6. clean code: use canonicalize_attrs instead of inlining the function;
7. add test cases for libpaddle.Scalar in python code.
8. add test cases for `make_scalar_proto`, which manipulate proto message `Scalar` via protobuffer python API.

* use iwyu clean include second time, test=develop