Reworked handling of implicit inline marking for member and friend
function defined in class.
Now, we handle it in an additive manner, i.e. if such in-class functions
are inline implicitly by language rules,
we mark the as `setImplicitInline`, and perform no action otherwise.
As we never remove inline specifier, the implementation is orthogonal to
other sources of inline
(like `inline`, `constexpr`, e.t.c), and we do not need to handle them
specially.
Also included test for `constexpr`, `consteval` and global module cases.
4ac141683c