QVersionNumber: Make documentation period display style consistent

In the current documentation for this class there are two ways that the
period character is referred to.

Code Style: https://doc.qt.io/qt-6/qversionnumber.html#fromString
Quote Style: https://doc.qt.io/qt-6/qversionnumber.html#fromString-1

The code-style version is significantly clearer and clean looking, while
the quote-style version is easy to misinterpret, especially when
followed by an additional period at the end of a sentence.

This change updates the documentation so that the nicer style is used in
all locations to improve clarity and consistency.

Change-Id: I11a6d82accb923e24c00b93728ea084d27efd06d
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/tools/qversionnumber.cpp

@@ -415,7 +415,7 @@ QString QVersionNumber::toString() const
     \since 6.4
 
     Constructs a QVersionNumber from a specially formatted \a string of
-    non-negative decimal numbers delimited by '.'.
+    non-negative decimal numbers delimited by a period (\c{.}).
 
     Once the numerical segments have been parsed, the remainder of the string
     is considered to be the suffix string.  The start index of that string will be