… test" (#3898)

Reverts #3889

The tree is red on a warning in the test code, most likely new in the Xcode version that the tree was just updated to. Reverting so we can re-land this with a fix for the new warning.

…image stream format (#3277)

### Note: this is a re-created PR from flutter/plugins#6985
---

This PR adds NV21 as an image stream format for android devices. This is the format required for things like MLKit. Unfortunately a lot of people tend to implement the yuv->nv21 incorrectly in dart, which results in countless issues of users saying the image stream doesn't work, or that mlkit doesn't work.

By allowing the plugin to send NV21 to dart, this will fix all of those yuv conversion issues.

Highlights:

-   Added an abstraction around `ImageReader` called `ImageStreamReader` and moved the image stream logic into this class to clean up the `Camera` class. This allows us to test the image stream handler in isolation.
-   Added tests for `ImageStreamReader` to make sure it only calls the `removePlaneBufferPadding` function for planes that contain padding.
-   Added a new utility class called `ImageStreamReaderUtils` which contains the logic for trimming the padding.
-   Added tests for `ImageStreamReaderUtils` to make sure it only removes padding when a given buffer contains padding to be removed.
-   There are tests to confirm both that `removePlaneBufferPadding` is only called when padding is present, and to confirm that if `removePlaneBufferPadding` does happen to be called with a buffer containing no padding, it still returns a valid buffer.

*List which issues are fixed by this PR. You must list at least one issue.*

- flutter/flutter#118350

*If you had to change anything in the [flutter/tests] repo, include a link to the migration guide as per the [breaking change policy].*

Removes lint-baseline.xml and fixes all warnings.

Part of flutter/flutter#88011

Removes lint-baseline.xml and fixes all exposed lints. Includes an update of Pigeon to the latest version, to pick up warning fixes in generated code.

Part of flutter/flutter#88011

…t test (#3901)

`as [Any?]` here is actually not a "cast", but a "type annotation". An equivalent fix can be: 

```
let arg: [Any?] = [nil]
let inputEncoded = binaryMessenger.codec.encode(arg)
```

Fixes
```
heterogeneous collection literal could only be inferred to '[Any?]'; add explicit type annotation if this is intentional
```

Which was introduced in #3889 and later got reverted. 

See flutter/flutter#126006 for more details about some interesting research on this warning. 

*List which issues are fixed by this PR. You must list at least one issue.*

Fixes flutter/flutter#126006

*If you had to change anything in the [flutter/tests] repo, include a link to the migration guide as per the [breaking change policy].*