chore: Allow drawer content to use full height

[jkuelz]

Description

This is a follow up from #2924 that addresses double scrollbar issue in Q chat panel (AWSUI-59823).
It also addresses an issue in Firefox where side nav would have a scrollbar when there was no side nav header present, the original reason for revert. The other issue regarding flashing scrollbar has been extracted from this PR.

Related links, issue #, if available: AWSUI-59823, TT: V1549419424, TT: D169004346,

How has this been tested?

Related screenshot tests added in CR-158701022
Ran through dev pipeline screenshot approvals:

• 1st: 833b9bfc-f87e-462e-b8e9-3d6f48d73c2a
• 2nd: 42b2f287-623e-4d54-ba8d-29edf66bea4d

Review checklist

The following items are to be evaluated by the author(s) and the reviewer(s).

Correctness

• Changes include appropriate documentation updates.
• Changes are backward-compatible if not indicated, see CONTRIBUTING.md.
• Changes do not include unsupported browser features, see CONTRIBUTING.md.
• Changes were manually tested for accessibility, see accessibility guidelines.

Security

• If the code handles URLs: all URLs are validated through the checkSafeUrl function.

Testing

• Changes are covered with new/existing unit tests?
• Changes are covered with new/existing integration tests?

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.27%. Comparing base (62f01ce) to head (901f404).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2986   +/-   ##
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  Coverage   96.27%   96.27%           
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  Files         769      769           
  Lines       21764    21768    +4     
  Branches     7038     7039    +1     
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+ Hits        20954    20958    +4     
  Misses        802      802           
  Partials        8        8           

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[just-boris]

Approved, but can be simplified further

[just-boris]

I did not find any condition when aria-hidden=true is applied on this selector. Does it mean we can remove that part of the selector?

[jkuelz]

Interesting, that feels unexpected because aria-hidden is set to !isOpen here. I would've expected it to change when the drawer is opened/closed, like it does for help panel and side nav.

It appears that isOpen always returns true because it is hardcoded this way. Not sure exactly when or what changed to make the isOpen condition obsolete. But I have removed this condition from the style.

[just-boris]

Why is this needed?

The default is flex-direction: row and I do not think we want this

[just-boris]

Discussed in DM, it relies on the default align-items: stretch behavior to stretch a single child.

Risky practice, but okay

[jkuelz]

There is only one child, so it's not actually aligning anything horizontally or vertically. But I can add a more explicit definition.

[just-boris]

Thank makes it easier to follow, thanks