ServerActionsGraph: pass ModuleGraphLayer as OperationVc (#94141)
### What?
Threads the layer module graph through `ServerActionsGraph` and
`map_server_actions` as an `OperationVc` instead of a resolved `Vc`,
calling `connect()` at each consumer.
### Why?
Fixes the invalidation priority of `map_server_actions` so it is
executed after the module graph on incremental builds. Previously,
because the graph was resolved at construction time, the dependency
ordering caused `map_server_actions` to be re-run before the module
graph on incremental rebuilds.
### How?
By passing the layer graph as an `OperationVc` and calling `connect()`
within each consumer task, the graph is resolved within the consuming
task rather than at construction time. This restores the intended
invalidation/scheduling order between the module graph and
`map_server_actions`.
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