Add `ExprTrait` (#771) (#791) #2221

Job	Run time
Build `sea-query`	46s
Clippy	34s
Build `sea-query-postgres`	33s
Build `sea-query-binder` (async-std, rustls)	44s
Build `sea-query-rusqlite`	35s
Rustfmt	10s
Unit Test	57s
Derive Tests	40s
MariaDB	0s
MySQL	0s
PostgreSQL	0s
Any	0s
SQLite	0s
	4m 59s

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