1. add a subdirectory named `cinn` in `paddle/fluid/operators` directory and move releated files into it
2. seperate CinnLaunchContext class from `cinn_launch_op.h` and put it in a  new independent file named `cinn_launch_context.h`, so that it can be included by others clearly.

* Add the `GetFetchNames` method in CinnGraphSymbolization.

* Use unordered_set instead vector as the type of fetch_var_names.

* Reuse the definition of kCompilationKey.

* Use CompileOptions to set fetch_var_ids.

* Update the argument passing of GraphCompiler.Build.

* Fix some bugs in CinnGraphSymbolization::GetFetchIds.

Add FLAGS_allow_cinn_ops & FLAGS_deny_cinn_ops for controlling op types used in training with CINN. (#36842)

* Update UT test_parallel_executor_run_cinn.py.

* Add FLAGS_allow_cinn_ops & FLAGS_deny_cinn_ops & FLAGS_cinn_ops_delim.

* Use the custom StringSplit function and remove the FLAGS_cinn_ops_delim flag.

* Add FlagController test.

* Apply lock to the cache_ only in CinnCompiler.

* Add VizGraph & ReadableKey method for CinnCompiler.

* Update the dot style of VizGraph in CinnCompiler.

* Init the functions of CinnCompiler.

* Add the unit test for CinnCompiler.

* Fix some compilation errors.

* Update the UT of cinn_compiler.

* Use Decomposer&OpFusion passes in CinnCompiler::CompileGraph.

* Update some comments.

* Uncomment some includes in build_cinn_pass.cc.

* Use refs instead of ptrs as returned types of FindGraph & Compile in
CinnCompiler.

* Use the merged CinnGraphSymbolization functions in CinnCompiler.