Inline member-swap functions of implicitly-shared classes

At least these classes have an out-of-line member-swap():

• QFutureInterfaceBase
• QHttp2Configuration (might need the out-of-line swap() d/to SmallData optimization?)
• QJsonDocument
• QJsonValue

Member-swap()'s should be inline.

Acceptance criteria:

• Fix the above-mentioned member-swap()s to be inline (QT_*_INLINE_SINCE)
• Scan all modules for other out-of-line member-swaps and fix those, too.