Update input system to 1.12.0

[megh-jagad]

Please read the Contributing guide before making a PR.

• Read the Graphics repository & Yamato FAQ.

Checklist for PR maker

• Have you added a backport label (if needed)? For example, the need-backport-* label. After you backport the PR, the label changes to backported-*.
• Have you updated the changelog? Each package has a CHANGELOG.md file.
• Have you updated or added the documentation for your PR? When you add a new feature, change a property name, or change the behavior of a feature, it's best practice to include related documentation changes in the same PR. If you do add documentation, make sure to add the relevant Graphics Docs team member as a reviewer of the PR. If you are not sure which person to add, see the Docs team contacts sheet.
• Have you added a graphic test for your PR (if needed)? When you add a new feature, or discover a bug that tests don't cover, please add a graphic test.

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Purpose of this PR

Update input system to 1.12.0 for 6000.1

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Testing status

Ran the test runner. No issues

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Comments to reviewers

[lyndon-unity]

Overall the change updates the necessary manifest and package files and project settings to be input system only. Happy to approve - made a small comment about the changelog message and alternative PR

[lyndon-unity]

We added a litte more in the alternative PR.

• Upgrade input system version to 1.12.0 so that a warning message is shown on platforms which require additional platform specific input system packages to be installed.
• Set InputHandler to input system exclusive

(See https://github.com/Unity-Technologies/Graphics/pull/8118/files)

[theopnv]

Just running the templates suite here before hitting merge https://unity-ci.cds.internal.unity3d.com/job/46317295.