Code cleanup: CHIPCertToX509. (#10931)

-- removed element type check from reader.Next() where it is later checked by reader.Get()
 -- removed size checks/adjustments around integer reader.Get().
    These checks are now performed by the Get() method itself.
 -- Added new Get(FixedByteSpan<N> & v) method to the TLVReader class.
 -- handle UTF8 DN attribute as CharSpan instead on ByteSpan.
 -- Switched to use VerifyOrReturnError() and ReturnErrorOnFailure() macros.

src/credentials/CHIPCert.cpp

@@ -575,7 +575,7 @@ CHIP_ERROR ChipDN::AddAttribute(chip::ASN1::OID oid, uint64_t val)
     return CHIP_NO_ERROR;
 }
 
-CHIP_ERROR ChipDN::AddAttribute(chip::ASN1::OID oid, ByteSpan val)
+CHIP_ERROR ChipDN::AddAttribute(chip::ASN1::OID oid, CharSpan val)
 {
     uint8_t rdnCount = RDNCount();
 

src/credentials/CHIPCert.h

@@ -196,7 +196,7 @@ enum
  */
 struct ChipRDN
 {
-    ByteSpan mString;         /**< Attribute value when encoded as a string. */
+    CharSpan mString;         /**< Attribute value when encoded as a string. */
     uint64_t mChipVal;        /**< CHIP specific DN attribute value. */
     chip::ASN1::OID mAttrOID; /**< DN attribute CHIP OID. */
 
@@ -231,12 +231,12 @@ class ChipDN
      * @brief Add string attribute to the DN.
      *
      * @param oid     String OID for DN attribute.
-     * @param val     A ByteSpan object containing a pointer and length of the DN string attribute
+     * @param val     A CharSpan object containing a pointer and length of the DN string attribute
      *                buffer. The value in the buffer should remain valid while the object is in use.
      *
      * @return Returns a CHIP_ERROR on error, CHIP_NO_ERROR otherwise
      **/
-    CHIP_ERROR AddAttribute(chip::ASN1::OID oid, ByteSpan val);
+    CHIP_ERROR AddAttribute(chip::ASN1::OID oid, CharSpan val);
 
     /**
      * @brief Determine type of a CHIP certificate.