stream-clone: add a explicit set list requirements relevant to stream clone
This set explicitly lists all the requirements that "stream clone" will
preserve. Any other one will not be preserved.
The role of listing the relevant one was previously filled by
`repo.supportedformat`, but it seems clearer to use that such global and
explicit set. The `repo.supportedformat` attribute will be cleaned up in a later
changeset
The true meaning of `repo.supportedformat` vs `repo._basesupported` was lost
over time so, the content is currently bad. For example, `dirstate-v2` is
currently considered relevant to the stream clone, or internal phase is
missing. We kept the same content in this changeset and we will fix them later.
Differential Revision: https://phab.mercurial-scm.org/D12032
local test passed
addgroupcopy test passed
clone test passed
lowlevelcopy test passed
slicing test passed
issnapshot test passed
findsnapshot test passed