Replaced isEmbeddedWebView with isAppContext

[AllanOXDi]

Summary

This Pr replaces the use of isEmbeddedWebView with isAppContext

• Added an isAppContext computed property to the core useUser composable
• Replaced every instance of isEmbeddedWebView with the isAppContext computed prop
• Deleted unused isEmbeddedWebView and the constituent values from browserInfo.js

References

#11689

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Reviewer guidance

Do these changes make sense ?

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Testing checklist

• Contributor has fully tested the PR manually
• If there are any front-end changes, before/after screenshots are included
• Critical user journeys are covered by Gherkin stories
• Critical and brittle code paths are covered by unit tests

PR process

• PR has the correct target branch and milestone
• PR has 'needs review' or 'work-in-progress' label
• If PR is ready for review, a reviewer has been added. (Don't use 'Assignees')
• If this is an important user-facing change, PR or related issue has a 'changelog' label
• If this includes an internal dependency change, a link to the diff is provided

Reviewer checklist

• Automated test coverage is satisfactory
• PR is fully functional
• PR has been tested for accessibility regressions
• External dependency files were updated if necessary (yarn and pip)
• Documentation is updated
• Contributor is in AUTHORS.md

[github-actions]

Build Artifacts

Asset type	Download link
PEX file	kolibri-0.16.0b10.dev0_git.509.g5aaab9a5.pex
Windows Installer (EXE)	kolibri-0.16.0b10.dev0+git.509.g5aaab9a5-unsigned.exe
Debian Package	kolibri_0.16.0b10.dev0+git.509.g5aaab9a5-0ubuntu1_all.deb
Mac Installer (DMG)	kolibri-0.16.0b10.dev0+git.509.g5aaab9a5-0.3.0.dmg
Android Package (APK)	kolibri-0.16.0b10.dev0+git.509.g5aaab9a5-0.1.0-debug.apk
TAR file	kolibri-0.16.0b10.dev0+git.509.g5aaab9a5.tar.gz
WHL file	kolibri-0.16.0b10.dev0+git.509.g5aaab9a5-py2.py3-none-any.whl

[rtibbles]

Most of the way there, just two things to clean up!

[rtibbles]

Logic got reversed in a couple of places, added suggestions to tweak.

[rtibbles]

Docs build failure is unrelated, merging!