clusterversion: reduce stuttering in package API

This package was extracted out of pkg/settings/cluster in #45455. Now
that we're coupling it tightly with our migrations infrastructure
(pkg/migration), let's remove some unnecessary stuttering for ease of
use.

```diff
- if <settings handle>.Version.IsActive(ctx, clusterversion.VersionSomething) {
+ if <settings handle>.Version.IsActive(ctx, clusterversion.Something) {
```

All the diffs here are just mechanical goland-renames.

Release note: None

pkg/ccl/backupccl/restore_job.go

@@ -1153,7 +1153,7 @@ func (r *restoreResumer) Resume(
 	details := r.job.Details().(jobspb.RestoreDetails)
 	p := execCtx.(sql.JobExecContext)
 	r.versionAtLeast20_2 = p.ExecCfg().Settings.Version.IsActive(
-		ctx, clusterversion.VersionLeasedDatabaseDescriptors)
+		ctx, clusterversion.LeasedDatabaseDescriptors)
 
 	backupManifests, latestBackupManifest, sqlDescs, err := loadBackupSQLDescs(
 		ctx, p, details, details.Encryption,

pkg/ccl/backupccl/restore_planning.go

@@ -1663,7 +1663,7 @@ func doRestorePlan(
 	//
 	// TODO(ajwerner): Remove this version check in 21.1.
 	canResetModTime := p.ExecCfg().Settings.Version.IsActive(
-		ctx, clusterversion.VersionLeasedDatabaseDescriptors)
+		ctx, clusterversion.LeasedDatabaseDescriptors)
 	if err := RewriteTableDescs(
 		tables, descriptorRewrites, intoDB, canResetModTime,
 	); err != nil {

pkg/ccl/importccl/import_stmt.go

@@ -1027,7 +1027,7 @@ func prepareNewTableDescsForIngestion(
 	}
 	// TODO(ajwerner): Remove this in 21.1.
 	canResetModTime := p.ExecCfg().Settings.Version.IsActive(
-		ctx, clusterversion.VersionLeasedDatabaseDescriptors)
+		ctx, clusterversion.LeasedDatabaseDescriptors)
 	if err := backupccl.RewriteTableDescs(
 		newMutableTableDescriptors, tableRewrites, "", canResetModTime,
 	); err != nil {

pkg/clusterversion/.gitattributes

@@ -1 +1 @@
-versionkey_string.go binary
+key_string.go binary

pkg/clusterversion/BUILD.bazel

@@ -6,10 +6,10 @@ go_library(
         "cluster_version.pb.go",
         "clusterversion.go",
         "cockroach_versions.go",
+        "key_string.go",
         "keyed_versions.go",
         "setting.go",
         "testutils.go",
-        "versionkey_string.go",
     ],
     importpath = "github.com/cockroachdb/cockroach/pkg/clusterversion",
     visibility = ["//visibility:public"],

pkg/clusterversion/clusterversion.go

@@ -99,7 +99,7 @@ type Handle interface {
 	// outbound requests. When receiving these "new" inbound requests, despite
 	// not seeing the latest active version, node2 is aware that the sending
 	// node has, and it will too, eventually.
-	IsActive(context.Context, VersionKey) bool
+	IsActive(context.Context, Key) bool
 
 	// BinaryVersion returns the build version of this binary.
 	BinaryVersion() roachpb.Version
@@ -206,7 +206,7 @@ func (v *handleImpl) SetActiveVersion(ctx context.Context, cv ClusterVersion) er
 }
 
 // IsActive implements the Handle interface.
-func (v *handleImpl) IsActive(ctx context.Context, key VersionKey) bool {
+func (v *handleImpl) IsActive(ctx context.Context, key Key) bool {
 	return version.isActive(ctx, v.sv, key)
 }
 
@@ -228,8 +228,8 @@ func (cv ClusterVersion) IsActiveVersion(v roachpb.Version) bool {
 
 // IsActive returns true if the features of the supplied version are active at
 // the running version.
-func (cv ClusterVersion) IsActive(versionKey VersionKey) bool {
-	v := VersionByKey(versionKey)
+func (cv ClusterVersion) IsActive(versionKey Key) bool {
+	v := ByKey(versionKey)
 	return cv.IsActiveVersion(v)
 }