[BUG] - MatFormField is injected without 'optional' flag

[jano-kucera]

MatFormField injection is not optional, even though logic using it handles it as optional.

Steps to reproduce the behavior:
Create the ngx-time-picker on input without a MatFormField on it and observe error.

Versions

• ngx-mat-timepicker version 21.0.0

[tonysamperi]

Related to #140.
So this basically affects users using a standard input when appendToInput is true.
We need to decide if keeping the MatFormField optional or not.

To my mind, this library was specifically born to work with Material.
Honestly I'm more inclined to leave as it is, despite the new behaviour was created unintentionally with commit 71bee9e.

In the end v21 was published 3 months ago (December 8th) and we got this reported only now. So I deduce the vast majority of people are actually using the lib with MatFormControl.

I'll leave this open for a bit longer, to see if more complaints pop up, but right know I would be for removing entirely the check and always rely on Material is the best course of action (also for best compatibility).

[jano-kucera]

We upgraded to v21 only now because of some other blocking libraries...

The reason we picked this time picker was that we have custom inputs, but using Material date pickers (which still DO work without MatFormField), and this time picker had the same behavior.