Set tab stop distance with tabStopDistance in Gui

[YakoYakoYokuYoku]

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PR Description

What type of PR is this? (Check one of the boxes below)

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
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What does this pull request do?

tabStopWidth was deprecated in Qt 5.10 and tabStopDistance is recommended to be used instead.

Show a few screenshots (if this is a visual change)

N/A.

Have you tested your changes (if applicable)? If so, how?

Built Natron and used the script editor.

Futher details of this pull request

Used horizontalAdvance from the font metrics to be coherent with the Qt recommendations, which in turn will be done in another PR too.
This was a blocker of one of the things I've been working on.

[rodlie]

There are two checks for >=QT_VERSION_CHECK(5, 11, 0) and one for >=QT_VERSION_CHECK(5, 10 0) on the same feature (added in 5.10), a typo?

[YakoYakoYokuYoku]

This is not a typo because QFontMetrics::horizontalAdvance was introduced in version 5.11.