move IsValid to ControllableContext (#4699)

<!-- Describe what has changed in this PR -->
**What changed?**
This moves the `IsValid` method from `shard.Context` to
`shard.ControllableContext`.

<!-- Tell your future self why have you made these changes -->
**Why?**
Only the shard controller needs to call `IsValid`.

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test? Checked in staging env? -->
**How did you test it?**
CI.

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change to production? -->
**Potential risks**
None.

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**Is hotfix candidate?**
No.

service/history/shard/context.go

@@ -57,7 +57,6 @@ type (
 	Context interface {
 		GetShardID() int32
 		GetRangeID() int64
-		IsValid() bool
 		GetOwner() string
 		GetExecutionManager() persistence.ExecutionManager
 		GetNamespaceRegistry() namespace.Registry
@@ -126,8 +125,9 @@ type (
 	// the Controller.
 	ControllableContext interface {
 		Context
-
 		common.Pingable
+
+		IsValid() bool
 		FinishStop()
 	}
 )

service/history/shard/controller_impl.go

@@ -231,7 +231,7 @@ func (c *ControllerImpl) shardRemoveAndStop(shard ControllableContext) {
 // getOrCreateShardContext returns a shard context for the given shard ID, creating a new one
 // if necessary. If a shard context is created, it will initialize in the background.
 // This function won't block on rangeid lease acquisition.
-func (c *ControllerImpl) getOrCreateShardContext(shardID int32) (Context, error) {
+func (c *ControllerImpl) getOrCreateShardContext(shardID int32) (ControllableContext, error) {
 	if err := c.validateShardId(shardID); err != nil {
 		return nil, err
 	}