Improve 'Clear Output' button position

[AdriaandeJongh]

With #112690, the output panel's buttons were changed to show horizontally, looking cleaner and better. However, one complaint was that this change would mess with people's muscle memory to find the Clear button, which is arguably the most used button in that container. That complaint was met (also by me) with "we'll just have to get used to it" and the PR was merged.

Having played with the dev and beta version a bit, and having resized the editor docks a fair amount playing with various layouts, it does bother me more than I thought it would that the button "moves" and isn't stuck to a corner.

Clear button position (master)	Screenshot
The minimum-sized output dock positions it all the way to the right because the HFlowContainer wraps the rest of the buttons to the next lines:
A slightly larger output dock moves the button closer to the left than the right:
A wide output dock positions it closer to the right:

In conclusion, one can't grow any muscle memory for the button any longer. This PR attempts to fix that.

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My first attempt to address this was to put the two buttons to the right. With this first attempt, the gestalt of the two buttons merges with the buttons below it, making a 2x2 grid of buttons, and... it's perhaps a bit awkward? Also, the Collapse and Expand Bottom Panel button icons look somewhat similar, which may pose a problem. So I concluded that perhaps we should move the clear button to the left instead? It doesn't look as sexy (in my opinion), but the button will always be on the left this way and will allow for muscle memory to grow again.

Clear button position (this PR)	Screenshot
First iteration: right
Second iteration: left
Third iteration: left (current state of this PR)

A few other small changes this PR does to improve the new output dock layout ever so slightly:

• applies the same theme variant to the clear and collapse buttons as the pin and keep open buttons in the bar below it.
• reduces the minimum size of the filter text field from 200 to 150 so that in theory the HFlowContainer never has to break the bar into two rows. I tried it with a few common languages and the text never seems to get cut off.
• reduces the minimum size of the output filter buttons from "MMM" to "MM".

[derket25]

I think both buttons should be moved to the left.

[arkology]

• reduces the minimum size of the filter text field from 200 to 150 so that in theory the HFlowContainer never has to break the bar into two rows. I tried it with a few common languages and the text never seems to get cut off.

Did you try to do Output window floating?
Context – minimum width of docks in bottom dock slot is specified not only by their own minimum size, but also by bottom dock "bar" (panel with docks names, engine version and so on). Also it depends on center dock slot width. So making window floating can give you real info about actual minimum size of the dock.

[AdriaandeJongh]

• reduces the minimum size of the filter text field from 200 to 150 so that in theory the HFlowContainer never has to break the bar into two rows. I tried it with a few common languages and the text never seems to get cut off.

Did you try to do Output window floating?

Yup! No issues; text never gets cut off with the common languages I tested.

[Repiteo]

Thanks!