feat: add @mention support in send box

[musale]

Follow up to #2873
Closes #2828

PR Type

Description of the changes

PR checklist

• Project builds (yarn build) and changes have been tested in at least two supported browsers (Edge + non-Chromium based browser)
• All public APIs (classes, methods, etc) have been documented following the jsdoc syntax
• Stories have been added and existing stories have been tested
• Added appropriate documentation. Docs PR:

• License header has been added to all new source files (yarn setLicense)
• Contains NO breaking changes

Other information

[github-actions]

🚀 New react-contoso sample application deployed here

[github-actions]

Package	Line Rate	Branch Rate	Complexity	Health
mgt-chat.src.statefulClient	100%	100%	0	✔
mgt-chat.src.utils	100%	90%	0	✔
mgt-components.dist.es6.components.mgt-agenda.src.components.mgt-agenda	14%	100%	0	❌
mgt-components.dist.es6.components.mgt-contact.src.components.mgt-contact	62%	100%	0	➖
mgt-components.dist.es6.components.mgt-file-list.mgt-file-upload.src.components.mgt-file-list.mgt-file-upload	43%	100%	0	❌
mgt-components.dist.es6.components.mgt-file-list.src.components.mgt-file-list	62%	100%	0	➖
mgt-components.dist.es6.components.mgt-file.src.components.mgt-file	61%	100%	0	➖
mgt-components.dist.es6.components.mgt-get.src.components.mgt-get	19%	100%	0	❌
mgt-components.dist.es6.components.mgt-login.src.components.mgt-login	64%	100%	0	➖
mgt-components.dist.es6.components.mgt-messages.src.components.mgt-messages	66%	100%	0	➖
mgt-components.dist.es6.components.mgt-organization.src.components.mgt-organization	46%	100%	0	❌
mgt-components.dist.es6.components.mgt-people-picker.src.components.mgt-people-picker	56%	100%	0	➖
mgt-components.dist.es6.components.mgt-people.src.components.mgt-people	72%	100%	0	➖
mgt-components.dist.es6.components.mgt-person-card.src.components.mgt-person-card	59%	33%	0	➖
mgt-components.dist.es6.components.mgt-person.src.components.mgt-person	53%	100%	0	➖
mgt-components.dist.es6.components.mgt-picker.src.components.mgt-picker	78%	100%	0	✔
mgt-components.dist.es6.components.mgt-planner.src.components.mgt-planner	55%	100%	0	➖
mgt-components.dist.es6.components.mgt-profile.src.components.mgt-profile	39%	100%	0	❌
mgt-components.dist.es6.components.mgt-search-box.src.components.mgt-search-box	83%	100%	0	✔
mgt-components.dist.es6.components.mgt-search-results.src.components.mgt-search-results	56%	100%	0	➖
mgt-components.dist.es6.components.mgt-tasks-base.src.components.mgt-tasks-base	86%	100%	0	✔
mgt-components.dist.es6.components.mgt-taxonomy-picker.src.components.mgt-taxonomy-picker	74%	100%	0	➖
mgt-components.dist.es6.components.mgt-teams-channel-picker.src.components.mgt-teams-channel-picker	62%	100%	0	➖
mgt-components.dist.es6.components.mgt-theme-toggle.src.components.mgt-theme-toggle	74%	100%	0	➖
mgt-components.dist.es6.components.mgt-todo.src.components.mgt-todo	78%	100%	0	✔
mgt-components.dist.es6.components.src.components	86%	100%	0	✔
mgt-components.dist.es6.components.sub-components.mgt-arrow-options.src.components.sub-components.mgt-arrow-options	76%	100%	0	✔
mgt-components.dist.es6.components.sub-components.mgt-dot-options.src.components.sub-components.mgt-dot-options	29%	100%	0	❌
mgt-components.dist.es6.components.sub-components.mgt-flyout.src.components.sub-components.mgt-flyout	40%	100%	0	❌
mgt-components.dist.es6.components.sub-components.mgt-spinner.src.components.sub-components.mgt-spinner	92%	100%	0	✔
mgt-components.dist.es6.graph.src.graph	36%	100%	0	❌
mgt-components.dist.es6.src	100%	100%	0	✔
mgt-components.dist.es6.styles.src.styles	73%	100%	0	➖
mgt-components.dist.es6.utils.src.utils	46%	100%	0	❌
mgt-components.src.components	84%	75%	0	✔
mgt-components.src.components.mgt-contact	68%	83%	0	➖
mgt-components.src.components.mgt-file	62%	100%	0	➖
mgt-components.src.components.mgt-file-list	46%	100%	0	❌
mgt-components.src.components.mgt-file-list.mgt-file-upload	49%	86%	0	❌
mgt-components.src.components.mgt-get	22%	100%	0	❌
mgt-components.src.components.mgt-messages	68%	100%	0	➖
mgt-components.src.components.mgt-organization	47%	100%	0	❌
mgt-components.src.components.mgt-person	84%	76%	0	✔
mgt-components.src.components.mgt-person-card	67%	48%	0	➖
mgt-components.src.components.mgt-picker	80%	100%	0	✔
mgt-components.src.components.mgt-profile	40%	100%	0	❌
mgt-components.src.components.mgt-tasks-base	87%	100%	0	✔
mgt-components.src.components.mgt-theme-toggle	100%	100%	0	✔
mgt-components.src.components.mgt-todo	79%	100%	0	✔
mgt-components.src.components.sub-components.mgt-flyout	72%	53%	0	➖
mgt-components.src.components.sub-components.mgt-spinner	100%	100%	0	✔
mgt-components.src.graph	40%	73%	0	❌
mgt-components.src.styles	92%	80%	0	✔
mgt-components.src.utils	82%	46%	0	✔
mgt-element.dist.es6.components.src.components	72%	74%	0	➖
mgt-element.dist.es6.mock.src.mock	91%	77%	0	✔
mgt-element.dist.es6.providers.src.providers	87%	83%	0	✔
mgt-element.dist.es6.src	91%	80%	0	✔
mgt-element.dist.es6.utils.src.utils	67%	73%	0	➖
mgt-element.src	93%	40%	0	✔
mgt-element.src.components	78%	100%	0	✔
mgt-element.src.mock	81%	56%	0	✔
mgt-element.src.providers	83%	91%	0	✔
mgt-element.src.utils	71%	90%	0	➖
Summary	60% (27986 / 46509)	71% (556 / 788)	0	➖

[github-actions]

🚀 New react-contoso sample application deployed here

[github-actions]

🚀 New react-contoso sample application deployed here

[sebastienlevert]

Why is this still stuck?

[musale]

Why is this still stuck?

I opened it to check why the 2 checks were not completing. Nothing is being blocked by the two checks so @Mnickii you can merge it in.

[Mnickii]

@sebastienlevert @musale Ok, I'll momentarily disable status checks for the mgt-chat branch to merge this, then re-enable them.