Merges tabs into frames object in windowStore

[NejcZdovc]

Submitter Checklist:

• Submitted a ticket for my issue if one did not already exist.
• Used Github auto-closing keywords in the commit message.
• Added/updated tests for this change (for new code or code which already has tests).
• Ran git rebase -i to squash commits (if needed).

Resolves #8689

Auditors: @bsclifton @bbondy

Test Plan:

• tests should be green
• check if dnd is working correctly
• check if tabs are rendering correctly
• check if audio icon, favicon, private icon is displayed correctly

Reviewer Checklist:

Tests

• Adequate test coverage exists to prevent regressions
• Tests should be independent and work correctly when run indivually or as a suite ref

[bsclifton]

There is also a ui.tabs object in windowStore that you may consider dumping in a follow up. It's used for storing the preview index. For an example see:
https://github.com/brave/browser-laptop/blob/master/app/sessionStore.js#L126

Left some comments which could also be done in a follow up. Otherwise, looks great 😄 👍

[bsclifton]

It might be better to create a reference for this (ex: const frame = this.props.frame) and then just pass the frame={frame}, instead of this.props.frame each time. This way, if it changes again, you only change one place

[bsclifton]

Same with all the stuff above; getting rid of all the duplicate this.props.

[NejcZdovc]

we will remove all this props in redux PR, so I think it's not necessary to do it right now.

[bsclifton]

SGTM 👍 😄