uic: use QStringLiteral() instead of QString::fromUtf8() where applicable

uic: use QStringLiteral() instead of QString::fromUtf8() where applicable

Many (most?) strings written aren't in fact UTF-8, and we can check at
compile-time which are and which aren't, so don't hard-code fromUtf8()
but use the much more efficient QStringLiteral() where applicable.

This is low-hanging fruit. This patch only optimises US-ASCII string
literals, not those that are latin-1 or even UTF-8, because that would
require more extensive changes to the original fixString() function.

Likewise, there are also other calls to QString::fromUtf8() being
generated (e.g. in the pixmap code) that could benefit from being
turned into QStringLiterals, but their code paths are more involved
than those this patch fixes.

This patch at least suffices in turning all the setObjectName()
arguments into QStringLiterals, which was the main goal.

The autotest baseline has been updated with the new expected results.

Change-Id: Ic1ef67f500f9ff92d36164d515f4e004ef2a10bc
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@nokia.com>