Enhancements on wasm function execution time statistic (#2985)

Enhance the statistic of wasm function execution time, or the performance
profiling feature:
- Add os_time_thread_cputime_us() to get the cputime of a thread,
  and use it to calculate the execution time of a wasm function
- Support the statistic of the children execution time of a function,
  and dump it in wasm_runtime_dump_perf_profiling
- Expose two APIs:
  wasm_runtime_sum_wasm_exec_time
  wasm_runtime_get_wasm_func_exec_time

And rename os_time_get_boot_microsecond to os_time_get_boot_us.

core/iwasm/interpreter/wasm_runtime.h

@@ -186,6 +186,8 @@ struct WASMFunctionInstance {
     uint64 total_exec_time;
     /* total execution count */
     uint32 total_exec_cnt;
+    /* children execution time */
+    uint64 children_exec_time;
 #endif
 };
 
@@ -432,6 +434,13 @@ wasm_instantiate(WASMModule *module, WASMModuleInstance *parent,
 void
 wasm_dump_perf_profiling(const WASMModuleInstance *module_inst);
 
+double
+wasm_summarize_wasm_execute_time(const WASMModuleInstance *inst);
+
+double
+wasm_get_wasm_func_exec_time(const WASMModuleInstance *inst,
+                             const char *func_name);
+
 void
 wasm_deinstantiate(WASMModuleInstance *module_inst, bool is_sub_inst);