der: add ClarifyWriter #1835
Description
I have a pretty well-written #[cfg(feature = "clarify")] - gated writer that pretty-prints DER.
Proposal: To add Encode::to_hex_clarify, that annotates tags and types.
Example of PKCS#15:
30 3E <!-- tag: SEQUENCE len: 62 type: AuthenticationObjectChoice -->
<!-- CHOICE: Pwd -->
<!-- field: common_object_attributes -->
30 1B <!-- tag: SEQUENCE len: 27 type: CommonObjectAttributes -->
<!-- field: label -->
0C 12 <!-- tag: UTF8String len: 18 type: String -->
41 75 74 68 65 6E 74 69 63 61 74 69 6F 6E 20 50
49 4E <!-- "Authentication PIN" -->
<!-- end: String -->
<!-- field: flags -->
03 02 <!-- tag: BIT STRING type: CommonObjectFlags -->
06
C0
<!-- field: auth_id -->
04 01 <!-- tag: OCTET STRING type: OctetString -->
05
<!-- field: user_consent -->
<!-- field: access_control_rules -->
<!-- field: current_lcs -->
<!-- end: CommonObjectAttributes -->
<!-- field: class_attributes -->
30 03 <!-- tag: SEQUENCE type: CommonAuthenticationObjectAttributes -->
<!-- field: auth_id -->
04 01 <!-- tag: OCTET STRING type: OctetString -->
01
<!-- field: auth_reference -->
<!-- field: se_identifier -->
<!-- field: subclass_attributes -->
<!-- field: type_attributes -->
A1 1A <!-- tag: CONTEXT-SPECIFIC [1] (constructed) len: 26
type: ContextSpecificExplicit<PasswordAttributes> -->
30 18 <!-- tag: SEQUENCE len: 24 type: PasswordAttributes -->
<!-- field: pwd_flags -->
03 03 <!-- tag: BIT STRING type: PasswordFlags -->
04
48 10
<!-- field: pwd_type -->
0A 01 <!-- tag: ENUMERATED type: PasswordType -->
01
<!-- field: min_length -->
02 01 <!-- tag: INTEGER type: IntegerInRange -->
04
<!-- field: stored_length -->
02 01 <!-- tag: INTEGER type: IntegerInRange -->
04
<!-- field: max_length -->
02 01 <!-- tag: INTEGER type: IntegerInRange -->
04
<!-- field: pwd_reference -->
80 01 <!-- tag: CONTEXT-SPECIFIC [0] (primitive) type: Reference -->
01
<!-- field: pad_char -->
<!-- field: last_password_change -->
<!-- field: path -->
30 02 <!-- tag: SEQUENCE type: Path -->
<!-- field: efid_or_tag_choice -->
04 00 <!-- tag: OCTET STRING type: EfidOrTagChoice -->
<!-- CHOICE: EfidOrPath -->
<!-- field: index -->
<!-- field: length -->
<!-- field: verif_data_history_length -->
<!-- field: cio_security_id -->
<!-- end: ContextSpecificExplicit<PasswordAttributes> -->
<!-- end: PasswordAttributes -->
<!-- end: AuthenticationObjectChoice -->