Feat: 添加 CommandStart 依赖注入参数 (#915)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: yanyongyu <42488585+yanyongyu@users.noreply.github.com>

nonebot/params.py

@@ -32,6 +32,7 @@ from nonebot.consts import (
     CMD_ARG_KEY,
     RAW_CMD_KEY,
     REGEX_GROUP,
+    CMD_START_KEY,
     REGEX_MATCHED,
 )
 
@@ -99,6 +100,15 @@ def CommandArg() -> Any:
     return Depends(_command_arg)
 
 
+def _command_start(state: T_State) -> str:
+    return state[PREFIX_KEY][CMD_START_KEY]
+
+
+def CommandStart() -> str:
+    """消息命令开头"""
+    return Depends(_command_start)
+
+
 def _shell_command_args(state: T_State) -> Any:
     return state[SHELL_ARGS]