Deprecate manual TTID / `SentryDisplayWidget`

[buenaflor]

Description

Current state

We currently allow two options:

• automatic ttid which calls addPostFrameCallback within didPush of the navigator observer
• manual ttid which calls addPostFrameCallback within a widget's initState that you need to wrap around the widget you want to measure from

Why deprecate the manual version?

After some tests I've come to the conclusion that the automatic version is more accurate than we think (see timeline), there is usually a difference of around 2-5ms (give or take) to the actual frame duration which is negligible.

By deprecating it / removing it in v9 we reduce complexity of the implementation and usage but still report accurate data.