Use enumer to generate String() methods for most enums (#25705)

We have many hand-written String() methods (and similar) for enums.
These require more maintenance and are more error-prone than using
automatically generated methods. In addition, the auto-generated
versions can be more efficient.

Here, we switch to using https://github.com/loggerhead/enumer, itself
a fork of https://github.com/diegostamigni/enumer, no longer maintained,
and a fork of the mostly standard tool
https://pkg.go.dev/golang.org/x/tools/cmd/stringer.
We use this fork of enumer for Go 1.20+ compatibility and because
we require the `-transform` flag to be able to generate
constants that match our current code base.

Some enums were not targeted for this change:

command/agentproxyshared/cache/api_proxy.go

@@ -16,6 +16,7 @@ import (
 	"github.com/hashicorp/vault/http"
 )
 
+//go:generate enumer -type=EnforceConsistency -trimprefix=EnforceConsistency
 type EnforceConsistency int
 
 const (
@@ -23,6 +24,7 @@ const (
 	EnforceConsistencyAlways
 )
 
+//go:generate enumer -type=WhenInconsistentAction -trimprefix=WhenInconsistent
 type WhenInconsistentAction int
 
 const (

command/agentproxyshared/cache/enforceconsistency_enumer.go

@@ -0,0 +1,49 @@
+// Code generated by "enumer -type=EnforceConsistency -trimprefix=EnforceConsistency"; DO NOT EDIT.
+
+package cache
+
+import (
+	"fmt"
+)
+
+const _EnforceConsistencyName = "NeverAlways"
+
+var _EnforceConsistencyIndex = [...]uint8{0, 5, 11}
+
+func (i EnforceConsistency) String() string {
+	if i < 0 || i >= EnforceConsistency(len(_EnforceConsistencyIndex)-1) {
+		return fmt.Sprintf("EnforceConsistency(%d)", i)
+	}
+	return _EnforceConsistencyName[_EnforceConsistencyIndex[i]:_EnforceConsistencyIndex[i+1]]
+}
+
+var _EnforceConsistencyValues = []EnforceConsistency{0, 1}
+
+var _EnforceConsistencyNameToValueMap = map[string]EnforceConsistency{
+	_EnforceConsistencyName[0:5]:  0,
+	_EnforceConsistencyName[5:11]: 1,
+}
+
+// EnforceConsistencyString retrieves an enum value from the enum constants string name.
+// Throws an error if the param is not part of the enum.
+func EnforceConsistencyString(s string) (EnforceConsistency, error) {
+	if val, ok := _EnforceConsistencyNameToValueMap[s]; ok {
+		return val, nil
+	}
+	return 0, fmt.Errorf("%s does not belong to EnforceConsistency values", s)
+}
+
+// EnforceConsistencyValues returns all values of the enum
+func EnforceConsistencyValues() []EnforceConsistency {
+	return _EnforceConsistencyValues
+}
+
+// IsAEnforceConsistency returns "true" if the value is listed in the enum definition. "false" otherwise
+func (i EnforceConsistency) IsAEnforceConsistency() bool {
+	for _, v := range _EnforceConsistencyValues {
+		if i == v {
+			return true
+		}
+	}
+	return false
+}

command/agentproxyshared/cache/wheninconsistentaction_enumer.go

@@ -0,0 +1,50 @@
+// Code generated by "enumer -type=WhenInconsistentAction -trimprefix=WhenInconsistent"; DO NOT EDIT.
+
+package cache
+
+import (
+	"fmt"
+)
+
+const _WhenInconsistentActionName = "FailRetryForward"
+
+var _WhenInconsistentActionIndex = [...]uint8{0, 4, 9, 16}
+
+func (i WhenInconsistentAction) String() string {
+	if i < 0 || i >= WhenInconsistentAction(len(_WhenInconsistentActionIndex)-1) {
+		return fmt.Sprintf("WhenInconsistentAction(%d)", i)
+	}
+	return _WhenInconsistentActionName[_WhenInconsistentActionIndex[i]:_WhenInconsistentActionIndex[i+1]]
+}
+
+var _WhenInconsistentActionValues = []WhenInconsistentAction{0, 1, 2}
+
+var _WhenInconsistentActionNameToValueMap = map[string]WhenInconsistentAction{
+	_WhenInconsistentActionName[0:4]:  0,
+	_WhenInconsistentActionName[4:9]:  1,
+	_WhenInconsistentActionName[9:16]: 2,
+}
+
+// WhenInconsistentActionString retrieves an enum value from the enum constants string name.
+// Throws an error if the param is not part of the enum.
+func WhenInconsistentActionString(s string) (WhenInconsistentAction, error) {
+	if val, ok := _WhenInconsistentActionNameToValueMap[s]; ok {
+		return val, nil
+	}
+	return 0, fmt.Errorf("%s does not belong to WhenInconsistentAction values", s)
+}
+
+// WhenInconsistentActionValues returns all values of the enum
+func WhenInconsistentActionValues() []WhenInconsistentAction {
+	return _WhenInconsistentActionValues
+}
+
+// IsAWhenInconsistentAction returns "true" if the value is listed in the enum definition. "false" otherwise
+func (i WhenInconsistentAction) IsAWhenInconsistentAction() bool {
+	for _, v := range _WhenInconsistentActionValues {
+		if i == v {
+			return true
+		}
+	}
+	return false
+}