Reformat and convert comments in asn1.h.

Some of the X509 functions are hard to document without first
documenting the ASN.1 types themselves. (ASN1_TYPE's goofy
representation is leaked everywhere.)

Change-Id: I0adcf055414925f9e39c8293cbd42d29f0db3143
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/44044
Reviewed-by: Adam Langley <agl@google.com>

.clang-format

@@ -10,6 +10,16 @@ PointerAlignment: Right
 IncludeBlocks: Preserve
 TypenameMacros: ['LHASH_OF', 'STACK_OF']
 StatementMacros:
+  - "DECLARE_ASN1_ALLOC_FUNCTIONS"
+  - "DECLARE_ASN1_ALLOC_FUNCTIONS_name"
+  - "DECLARE_ASN1_ENCODE_FUNCTIONS"
+  - "DECLARE_ASN1_ENCODE_FUNCTIONS_const"
+  - "DECLARE_ASN1_FUNCTIONS"
+  - "DECLARE_ASN1_FUNCTIONS_const"
+  - "DECLARE_ASN1_FUNCTIONS_fname"
+  - "DECLARE_ASN1_FUNCTIONS_name"
+  - "DECLARE_ASN1_PRINT_FUNCTION"
+  - "DECLARE_ASN1_PRINT_FUNCTION_fname"
   - "DECLARE_PEM_read"
   - "DECLARE_PEM_read_bio"
   - "DECLARE_PEM_read_fp"