ledger: refactor evaluator into an internal package (algorand#2983)

## Summary

This PR reorganize the files inside the ledger package by move the evaluator related files into its own `internal` package.
The files in the internal package cannot access the root ledger files, and therefore using the shared `ledgercore` as a place to share interfaces.

```
ledger/
├── apply/
├── internal/
├── ledgercore/
└── testing/
```

## Test Plan

use existing test, and update existing tests.

Author: tsachiherman

compactcert/builder.go

@@ -45,7 +45,7 @@ type Builder struct {
 	sigs          []sigslot // Indexed by pos in participants
 	sigsHasValidL bool      // The L values in sigs are consistent with weights
 	signedWeight  uint64    // Total weight of signatures so far
-	participants  []Participant
+	participants  []basics.Participant
 	parttree      *merklearray.Tree
 
 	// Cached cert, if Build() was called and no subsequent
@@ -57,7 +57,7 @@ type Builder struct {
 // to be signed, as well as other security parameters, are specified in
 // param.  The participants that will sign the message are in part and
 // parttree.
-func MkBuilder(param Params, part []Participant, parttree *merklearray.Tree) (*Builder, error) {
+func MkBuilder(param Params, part []basics.Participant, parttree *merklearray.Tree) (*Builder, error) {
 	npart := len(part)
 
 	b := &Builder{

compactcert/builder_test.go

@@ -36,7 +36,7 @@ func (m TestMessage) ToBeHashed() (protocol.HashID, []byte) {
 }
 
 type PartCommit struct {
-	participants []Participant
+	participants []basics.Participant
 }
 
 func (pc PartCommit) Length() uint64 {
@@ -78,10 +78,10 @@ func TestBuildVerify(t *testing.T) {
 	// Share the key; we allow the same vote key to appear in multiple accounts..
 	key := crypto.GenerateOneTimeSignatureSecrets(0, 1)
 
-	var parts []Participant
+	var parts []basics.Participant
 	var sigs []crypto.OneTimeSignature
 	for i := 0; i < npartHi; i++ {
-		part := Participant{
+		part := basics.Participant{
 			PK:          key.OneTimeSignatureVerifier,
 			Weight:      uint64(totalWeight / 2 / npartHi),
 			KeyDilution: 10000,
@@ -91,7 +91,7 @@ func TestBuildVerify(t *testing.T) {
 	}
 
 	for i := 0; i < npartLo; i++ {
-		part := Participant{
+		part := basics.Participant{
 			PK:          key.OneTimeSignatureVerifier,
 			Weight:      uint64(totalWeight / 2 / npartLo),
 			KeyDilution: 10000,
@@ -165,12 +165,12 @@ func BenchmarkBuildVerify(b *testing.B) {
 		SecKQ:        128,
 	}
 
-	var parts []Participant
+	var parts []basics.Participant
 	var partkeys []*crypto.OneTimeSignatureSecrets
 	var sigs []crypto.OneTimeSignature
 	for i := 0; i < npart; i++ {
 		key := crypto.GenerateOneTimeSignatureSecrets(0, 1)
-		part := Participant{
+		part := basics.Participant{
 			PK:          key.OneTimeSignatureVerifier,
 			Weight:      uint64(totalWeight / npart),
 			KeyDilution: 10000,

compactcert/msgp_gen.go

@@ -30,34 +30,6 @@ type Params struct {
 	SecKQ        uint64          // Security parameter (k+q) from analysis document
 }
 
-// A Participant corresponds to an account whose AccountData.Status
-// is Online, and for which the expected sigRound satisfies
-// AccountData.VoteFirstValid <= sigRound <= AccountData.VoteLastValid.
-//
-// In the Algorand ledger, it is possible for multiple accounts to have
-// the same PK.  Thus, the PK is not necessarily unique among Participants.
-// However, each account will produce a unique Participant struct, to avoid
-// potential DoS attacks where one account claims to have the same VoteID PK
-// as another account.
-type Participant struct {
-	_struct struct{} `codec:",omitempty,omitemptyarray"`
-
-	// PK is AccountData.VoteID.
-	PK crypto.OneTimeSignatureVerifier `codec:"p"`
-
-	// Weight is AccountData.MicroAlgos.
-	Weight uint64 `codec:"w"`
-
-	// KeyDilution is AccountData.KeyDilution() with the protocol for sigRound
-	// as expected by the Builder.
-	KeyDilution uint64 `codec:"d"`
-}
-
-// ToBeHashed implements the crypto.Hashable interface.
-func (p Participant) ToBeHashed() (protocol.HashID, []byte) {
-	return protocol.CompactCertPart, protocol.Encode(&p)
-}
-
 // CompactOneTimeSignature is crypto.OneTimeSignature with omitempty
 type CompactOneTimeSignature struct {
 	_struct struct{} `codec:",omitempty,omitemptyarray"`
@@ -87,8 +59,8 @@ func (ssc sigslotCommit) ToBeHashed() (protocol.HashID, []byte) {
 type Reveal struct {
 	_struct struct{} `codec:",omitempty,omitemptyarray"`
 
-	SigSlot sigslotCommit `codec:"s"`
-	Part    Participant   `codec:"p"`
+	SigSlot sigslotCommit      `codec:"s"`
+	Part    basics.Participant `codec:"p"`
 }
 
 // MaxReveals is a bound on allocation and on numReveals to limit log computation