Observation of the Crab Nebula with LHAASO-KM2A − a performance study *Supported in China by National Key R&D program of China under the grants (2018YFA0404201, 2018YFA0404202, 2018YFA0404203), by NSFC (12022502, 11905227, 11635011, 11761141001, U1931112, 11775131, U1931201, 11905043, U1931108), by NSFSPC (ZR2019MA014), and in Thailand by RTA6280002 from Thailand Science Research and Innovation. (February 2021)