Make text containers wider in the Volume Change dialog

[srifqi]

Goal of the PR
This PR tries to make some texts' container in the Volume Change dialog wider to account for translations.

How does the PR work?
This PR changes dimensions of some GUI elements in the Volume Change dialog:

Element	Before	After
Sound Volume: 50% text	160 × 20	300 × 20
Muted checkbox	160 × 20	300 × 20
Exit button	80 × 30	100 × 30

Those dimensions are set to match the scroll bar width (and in turns making those texts look left-aligned).

Does it resolve any reported issue?
Not reported. Some translations get chopped off/wrapped in the Volume Change dialog. See below for examples.

Does this relate to a goal in the roadmap?
Yes, this PR tries to create a better UI/UX.

To do

This PR is Ready for Review.

How to test

1. Set Minetest language to other languages with long string/text for sound volume.
2. Start/restart Minetest to apply the language setting.
3. Play in a world/server.
4. Open the Pause menu (Esc key).
5. Open the Volume Change dialog (click the Sound Volume button).
6. Read the text. Make sure that the text is not chopped/wrapped.

Test results

Lang.	Before	After
es
fi
fil
ru