some flags, like "enable_stitch_fusion" and "enable_parallel_fusion", are enabled by default when opt_level=3.
and user can manually disable these flags.

Refactor the original "PassManager" class, and derive the "GraphKernelPassManager"
GraphKernel's ir files are dumped into a new sub-directory "graph_kernel" in the original "verbose_ir_files"

All GraphKernel's passes are divided into 3 levels, and controlled by the flag "opt_level" by default.
when the opt_level is greaterequal to the pass's level, this pass will run.
The default "opt_level" is 2 when GraphKernel is enabled.
Levels:
  1. Basic features, like cluster, splitter, and some preprocess, postprocess.
  2. All stable features, mainly includes the optimization passes.
  3. Experimental features, like stitch-fusion, parallel-fusion.

The two flags "enable_pass" and "disable_pass" are available in this commit.
User can manually enable some passes when it's disabled by "opt_level", or disable the enabled passes,
by specifying that pass in this format: "stage_id.pass_id" or "stage_name.pass_name", multiple passes are separated by comma(",")
the stage/pass index and stage/pass name can be found from the ir filename.
e.g.   "--enable_pass=cluster.graph_kernel_expander,1.1,1.2"

Others:
  1. the pass "tensor_promotion" is not useful, remove it.
  2. put the pass "InsertPadOps" before "ArithmeticSimplify".

used the flag "opt_level" to control GraphKernel,
0 means disabled while non-zero value means enabled.
the default value is controlled by context "enable_graph_kernel",
but if it's also set in "graph_kernel_flags", then the flag will prevail.

supported the whitelist and blacklist operators for GraphKernelExpander.
"enable_expand_ops", "enable_expand_ops_only", "disable_expand_ops".