…S 26 simulator (#188374)

This pull request is created by [automatic cherry pick workflow](https://github.com/flutter/flutter/blob/main/docs/releases/Flutter-Cherrypick-Process.md#automatically-creates-a-cherry-pick-request)
Please fill in the form below, and a flutter domain expert will evaluate this cherry pick request.

### Issue Link:
What is the link to the issue this cherry-pick is addressing?

#172864

### Impact Description:
Without this cherry-pick, the stable channel CI infrastructure cannot run its macOS and iOS simulator tests using Xcode 26 and macOS 15. This blocks upgrading the stable branch's CI pools to newer macOS/Xcode versions and leaves them running on older versions.

### Changelog Description:
Explain this cherry pick:
* In one line that is accessible to most Flutter developers.
* That describes the state prior to the fix.
* That includes which platforms are impacted.
See [best practices](https://github.com/flutter/flutter/blob/main/docs/releases/Hotfix-Documentation-Best-Practices.md) for examples.

< Replace with changelog description here >
[flutter/172864] Run stable channel macOS tests on macOS 15 and Xcode 26.

### Workaround:
No workaround exists as this affects the CI infrastructure configurations.

< Replace with workaround here >

### Risk:
What is the risk level of this cherry-pick?

### Test Coverage:
Are you confident that your fix is well-tested by automated tests?

### Validation Steps:
What are the steps to validate that this fix works?

CI builders for the stable branch (specifically macOS and iOS simulator shards) should pass successfully when using macOS 15 and Xcode 26.

This pull request is created by [automatic cherry pick workflow](https://github.com/flutter/flutter/blob/main/docs/releases/Flutter-Cherrypick-Process.md#automatically-creates-a-cherry-pick-request)

### Issue Link:
#188192

### Impact Description:
Flutter Linux apps could crash if a Linux accessibility client sent incorrect requests.

### Changelog Description:

[flutter/188192] Fix bounds checking in Flutter Linux's FlAccessibleTextField

### Workaround:
None

### Risk:
What is the risk level of this cherry-pick?

### Test Coverage:
Are you confident that your fix is well-tested by automated tests?

### Validation Steps:
On Linux, use an accessibility tool to interact with a Flutter app that has a text field.

Updates the engine.version file from `a4ce257c68517c1410f4b48ac9852ab5642a3f8d` to `a10d8ac38de835021c8d2f920dbf50a920ccc030`.

This pull request is created by [automatic cherry pick workflow](https://github.com/flutter/flutter/blob/main/docs/releases/Flutter-Cherrypick-Process.md#automatically-creates-a-cherry-pick-request)
Please fill in the form below, and a flutter domain expert will evaluate this cherry pick request.

### Issue Link:
What is the link to the issue this cherry-pick is addressing?

#186090

### Impact Description:
Updating CI to use either iOS 18 or 26 for easy transition when we update our devicelab bots

< Replace with impact description here >

### Changelog Description:
Explain this cherry pick:
* In one line that is accessible to most Flutter developers.
* That describes the state prior to the fix.
* That includes which platforms are impacted.
See [best practices](https://github.com/flutter/flutter/blob/main/docs/releases/Hotfix-Documentation-Best-Practices.md) for examples.

< Replace with changelog description here >
[flutter/<ISSUE_NUMBER>] When <SCENARIO> [on <PLAFORMS(S)>], <DESCRIPTION>

### Workaround:
Is there a workaround for this issue?

n/a

### Risk:
What is the risk level of this cherry-pick?

### Test Coverage:
Are you confident that your fix is well-tested by automated tests?

### Validation Steps:
What are the steps to validate that this fix works?

< Replace with validation steps here >

Updates the changelog for 3.44.4 stable hotfix.

Includes #188460

Excluded #188457 because it's an internal CI change