Add fixed(L) type to variant spec

Author: aihuaxu

VariantEncoding.md

@@ -399,6 +399,7 @@ The Decimal type contains a scale, but no precision. The implied precision of a
 | Timestamp            | timestamp with time zone   | `22`    | TIMESTAMP(isAdjustedToUTC=true, NANOS)       | 8-byte little-endian                                                                        |
 | TimestampNTZ         | timestamp without time zone | `23`    | TIMESTAMP(isAdjustedToUTC=false, NANOS)      | 8-byte little-endian                                                                        |
 | UUID                 | uuid                        | `24`    | UUID                         | 16-byte big-endian                                                                         |
+| Fixed(L)             | Byte array of length L | `25`    | FIXED_LEN_BYTE_ARRAY[L]     |  4 byte little-endian size L, followed by length-L bytes    |
 
 The *Type Equivalence Class* column indicates logical equivalence of physically encoded types.
 For example, a user expression operating on a string value containing "hello" should behave the same, whether it is encoded with the short string optimization, or long string encoding.