Convert all the call sites which use `g_memdup()`’s length argument
trivially (for example, by passing a `sizeof()` or an existing `gsize`
variable), so that they use `g_memdup2()` instead.

In almost all of these cases the use of `g_memdup()` would not have
caused problems, but it will soon be deprecated, so best port away from
it

In particular, this fixes an overflow within `g_bytes_new()`, identified
as GHSL-2021-045 by GHSL team member Kevin Backhouse.

Signed-off-by: Philip Withnall <pwithnall@endlessos.org>
Fixes: GHSL-2021-045
Helps: #2319