The function `GetByBean` has an obvious defect that when the fields are
empty values, it will be ignored. Then users will get a wrong result
which is possibly used to make a security problem.
To avoid the possibility, this PR removed function `GetByBean` and all
references.
And some new generic functions have been introduced to be used.
The recommand usage like below.
```go
// if query an object according id
obj, err := db.GetByID[Object](ctx, id)
// query with other conditions
obj, err := db.Get[Object](ctx, builder.Eq{"a": a, "b":b})
```
