proto: add proto files for ibc unblock (#4853)

## Description

these proto files are meant to help unblock ibc in their quest of migrating the ibc module to proto.

Closes: #XXX

libs/bits/bit_array.go

@@ -9,6 +9,7 @@ import (
 
 	tmmath "github.com/tendermint/tendermint/libs/math"
 	tmrand "github.com/tendermint/tendermint/libs/rand"
+	tmprotobits "github.com/tendermint/tendermint/proto/libs/bits"
 )
 
 // BitArray is a thread-safe implementation of a bit array.
@@ -418,3 +419,28 @@ func (bA *BitArray) UnmarshalJSON(bz []byte) error {
 	*bA = *bA2 //nolint:govet
 	return nil
 }
+
+// ToProto converts BitArray to protobuf
+func (bA *BitArray) ToProto() *tmprotobits.BitArray {
+	if bA == nil || len(bA.Elems) == 0 {
+		return nil
+	}
+
+	return &tmprotobits.BitArray{
+		Bits:  int64(bA.Bits),
+		Elems: bA.Elems,
+	}
+}
+
+// FromProto sets a protobuf BitArray to the given pointer.
+func (bA *BitArray) FromProto(protoBitArray *tmprotobits.BitArray) {
+	if protoBitArray == nil {
+		bA = nil
+		return
+	}
+
+	bA.Bits = int(protoBitArray.Bits)
+	if len(protoBitArray.Elems) > 0 {
+		bA.Elems = protoBitArray.Elems
+	}
+}

libs/bits/bit_array_test.go

@@ -265,3 +265,26 @@ func TestJSONMarshalUnmarshal(t *testing.T) {
 		})
 	}
 }
+
+func TestBitArrayProtoBuf(t *testing.T) {
+	testCases := []struct {
+		msg     string
+		bA1     *BitArray
+		expPass bool
+	}{
+		{"success empty", &BitArray{}, true},
+		{"success", NewBitArray(1), true},
+		{"success", NewBitArray(2), true},
+		{"negative", NewBitArray(-1), false},
+	}
+	for _, tc := range testCases {
+		protoBA := tc.bA1.ToProto()
+		ba := new(BitArray)
+		ba.FromProto(protoBA)
+		if tc.expPass {
+			require.Equal(t, tc.bA1, ba, tc.msg)
+		} else {
+			require.NotEqual(t, tc.bA1, ba, tc.msg)
+		}
+	}
+}