[HDRP] Fix camera not loosing focus when pressing [esc]

[alelievr]

Purpose of this PR

Add esc control to release the cursor when entering play mode in the template of HDRP.

https://forum.unity.com/threads/hdrp-template-esc-clicking-outside-of-viewport-doesnt-unfocus.1130944/

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Testing status

Tested that the escape key and right/left click works as intended to respectively release and attach the focus:

With the new InputSystem:

MouseFocus.mp4

With the old one:

MouseFocusOld.mp4

[github-actions]

Hi! This comment will help you figure out which jobs to run before merging your PR. The suggestions are dynamic based on what files you have changed.
Link to Yamato: https://yamato.cds.internal.unity3d.com/jobs/902-Graphics
Search for your PR branch using the sidebar on the left, then add the following segment(s) to the end of the URL (you may need multiple tabs depending on how many packages you change)

HDRP
/.yamato%252Fall-hdrp.yml%2523PR_HDRP_2021.2

Depending on the scope of your PR, you may need to run more jobs than what has been suggested. Please speak to your lead or a Graphics SDET (#devs-graphics-automation) if you are unsure.

[RemyUnity]

Thank you for the video showcase, LGTM 🟢