[react] Mark Config contravariant and Instance covariant in AbstractComponent
[react] Mark Config contravariant and Instance covariant in AbstractComponent

Summary:
Since we check Config contravariantly and Instance covariantly, we should be allowed to use a
contravariant/covariant type parameter in those positions. This will be tested in a stacked diff that adds
a type alias to the libdefs with these properties.

Reviewed By: samwgoldman

Differential Revision: D13221118

fbshipit-source-id: d3b8a50ae571d2e8d40f72c4f802f2b5218d6bf3

AgentME/flow,popham/flow,popham/flow,gabelevi/flow,samwgoldman/flow,samwgoldman/flow,mroch/flow,mroch/flow,AgentME/flow,mroch/flow,mroch/flow,popham/flow,popham/flow,gabelevi/flow,AgentME/flow,samwgoldman/flow,popham/flow,samwgoldman/flow,facebook/flow,facebook/flow,facebook/flow,gabelevi/flow,facebook/flow,AgentME/flow,facebook/flow,mroch/flow,gabelevi/flow,samwgoldman/flow,samwgoldman/flow,facebook/flow,gabelevi/flow,popham/flow,samwgoldman/flow,gabelevi/flow,mroch/flow,gabelevi/flow,facebook/flow,popham/flow,AgentME/flow,mroch/flow