## Part of #3062, related to #3435
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## PR Type
What kind of change does this PR introduce?
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- Optimization
- Deprecation
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<!-- - Feature -->
<!-- - Code style update (formatting) -->
<!-- - Refactoring (no functional changes, no api changes) -->
<!-- - Build or CI related changes -->
<!-- - Documentation content changes -->
<!-- - Sample app changes -->
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## What is the current behavior?
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The `Microsoft.Toolkit` package has a number of extensions for 2D arrays that are inefficient (they're both a bit slow and causing unnecessary memory allocations) and replaced by equivalent APIs in the `Microsoft.Toolkit.HighPerformance` package.
30452cf0bb/Microsoft.Toolkit/Extensions/ArrayExtensions.cs (L27)30452cf0bb/Microsoft.Toolkit/Extensions/ArrayExtensions.cs (L48)30452cf0bb/Microsoft.Toolkit/Extensions/ArrayExtensions.cs (L68)
## What is the new behavior?
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This PR makes these APIs obsolete, and also includes a number of small optimizations to existing code that was added during the refactoring to remove dependencies on these APIs, so that it'll be possible to remove them in the future with no issues.
## PR Checklist
Please check if your PR fulfills the following requirements:
- [X] Tested code with current [supported SDKs](../readme.md#supported)
- [ ] Pull Request has been submitted to the documentation repository [instructions](..\contributing.md#docs). Link: <!-- docs PR link -->
- [ ] ~~Sample in sample app has been added / updated (for bug fixes / features)~~
- [ ] ~~Icon has been created (if new sample) following the [Thumbnail Style Guide and templates](https://github.com/windows-toolkit/WindowsCommunityToolkit-design-assets)~~
- [X] Tests for the changes have been added (for bug fixes / features) (if applicable)
- [X] Header has been added to all new source files (run *build/UpdateHeaders.bat*)
- [X] Contains **NO** breaking changes
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## Fixes https://github.com/windows-toolkit/WindowsCommunityToolkit/issues/3536
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## PR Type
What kind of change does this PR introduce?
<!-- Please uncomment one or more that apply to this PR. -->
- Bugfix
<!-- - Feature -->
<!-- - Code style update (formatting) -->
<!-- - Refactoring (no functional changes, no api changes) -->
<!-- - Build or CI related changes -->
<!-- - Documentation content changes -->
<!-- - Sample app changes -->
<!-- - Other... Please describe: -->
## What is the current behavior?
<!-- Please describe the current behavior that you are modifying, or link to a relevant issue. -->
Seeking to the end of a `Stream` from a `Memory<T>` or other types in the `HighPerformance` package throws an exception.
## What is the new behavior?
<!-- Describe how was this issue resolved or changed? -->
Seeking to the end of the stream is now allowed. This is consistent to other `Stream` types in the BCL.
## PR Checklist
Please check if your PR fulfills the following requirements:
- [X] Tested code with current [supported SDKs](../readme.md#supported)
- [ ] ~~Pull Request has been submitted to the documentation repository [instructions](..\contributing.md#docs). Link: <!-- docs PR link -->~~
- [ ] ~~Sample in sample app has been added / updated (for bug fixes / features)~~
- [ ] ~~Icon has been created (if new sample) following the [Thumbnail Style Guide and templates](https://github.com/windows-toolkit/WindowsCommunityToolkit-design-assets)~~
- [X] Tests for the changes have been added (for bug fixes / features) (if applicable)
- [X] Header has been added to all new source files (run *build/UpdateHeaders.bat*)
- [X] Contains **NO** breaking changes
