fix(layout): some flex directives don't work when on a child of layout="column" or layout="row"

[Splaktar]

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• The commit message follows our guidelines
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PR Type

What kind of change does this PR introduce?

[x] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ ] Infrastructure changes
[ ] Other... Please describe:

What is the current behavior?

Some flex directives don't work when on a child of layout="column" or layout="row". This includes flex="0", flex="33", flex="66", flex="100".

Issue Number:
Fixes #9546

What is the new behavior?

flex="0", flex="33", flex="66", flex="100" now behave properly when applied to an element that is a child of an element with layout="column" or layout="row".

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

Relates to and includes contents of PR #10797.

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[Splaktar]

I reviewed the primary changes to the SCSS in #10797 and they LGTM. This PR just adds some whitespace cleanup and clarification to some comments.