Fix proto3 repeated field encoding without packed option

[osa1]

proto3 repeated fields are packed by default, see
https://developers.google.com/protocol-buffers/docs/encoding#packed.

Fixes #345

[sigurdm]

Should this instead throw an argument-error (is it not an error to ask if a non-repeated field is packed?)

[osa1]

The call site is this:

protobuf.dart/protoc_plugin/lib/src/protobuf_field.dart

Lines 157 to 169 in ad3f06f

	String get typeConstant {
	var prefix = 'O';
	if (isRequired) {
	prefix = 'Q';
	} else if (isPacked) {
	prefix = 'K';
	} else if (isRepeated) {
	prefix = 'P';
	}
	return '$protobufImportPrefix.PbFieldType.' +
	prefix +
	baseType.typeConstantSuffix;
	}

We don't check whether the field is repeated before checking whether it's packed. We could update the checks in the call site and expect repeated field here. I don't have an opinion on whether that would be an improvement or not because there's only one use site. We could even inline this getter.

[sigurdm]

Looking at the call-site it makes sense to just return false here I think.

I would prefer not inlining this amount of logic.

[sigurdm]

LGTM

[osa1]

@sigurdm PTAL. ProtobufField is refactored to use the new parent field.

[sigurdm]

LGTM

[osa1]

Ported to internal in cl/449702819.