Earlier than 1.19, if you summon a Villager with {VillagerData:{level:x < 5}} and trade with him, you can give him experience from current level to the highest one. At present, however, the experience he get is counted from 0 rather than the current level experience he should has.

How to Produce

• Run: /summon minecraft:villager ~ ~ ~ {VillagerData:{profession:cleric,level:4}} - You'll get an Expert (专家) Cleric (牧师).
• Trade with him.

      (×) The experience is counted from 0 rather 'an current, no matter whether is he has binded a workstation. You can watch the white bar above to judge.