KSqueezedTextLabel: Squeeze text when changing indent or margin

Summary:
When the label is not able to resize in a given layout and calls to
setIndent or setMargin further reduce the space available, the text
should be squeezed. Qt does not always send a resize event which would notify
us to squeeze the text. Therefore, these functions need
reimplementations adding manual calls to squeezeTextToLabel.

This fixes the autotest testChrome failing only on the CI (see T6982).

Test Plan:

• ksqueezedtextlabelautotest passes locally and with xvfb-run -s '-screen 0 800x600x24'
• abi-compliance-checker suggests the changes are binary compatible

Reviewers: Frameworks, dhaumann, cfeck

Reviewed By: cfeck

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D7977