We should provide the completion when the cursor is in the attribute
name after the `@` and `animate-`, but now the `KeySpan` starts from the
`@` or `animate-`. For example, the animation event `(@name.done)="v"`,
we can know where the cursor is by the `KeySpan` of `name.done` exactly,
it's in the event name or in the phase name.
PR Close#40347