TpAccountChannelRequest: copy the hash table with a specific memory model
TpAccountChannelRequest: copy the hash table with a specific memory model

Forcing use of a particular key and value destructor makes it safe to
edit the hash table after the request has been created. (Setting every
property in the constructor doesn't scale, in the presence of optional
properties, and we want high-level API for this so apps can be a bit
less D-Bus-API-dependent.)

Signed-off-by: Simon McVittie <2b470b34502dbf3ba4bcc04ea7e64f4e0e104f33@collabora.co.uk>
Reviewed-by: Jonny Lamb <3d1fb3642aaab2ff70e3392a5ab916bf99eed6a3@collabora.co.uk>
Bug: https://bugs.freedesktop.org/show_bug.cgi?id=48780

Distrotech/telepathy-glib,Distrotech/telepathy-glib,Distrotech/telepathy-glib,Distrotech/telepathy-glib,Distrotech/telepathy-glib