Support parsing v128.const i64x2 0 0 in #parse_numeric_instruction

This is the only vector instruction which appears in test/core/*.wast
(and was only added yesterday [0]) so it’s not yet worth properly
implementing the instruction in general. The one occurrence in
linking.wast uses `i64x2` as its shape descriptor [1] so here we read
two numbers (actually zeros) after reading the instruction and shape.

[0] WebAssembly/spec#1597
[1] https://webassembly.github.io/spec/core/syntax/instructions.html#syntax-vec-shape

lib/wasminna/ast_parser.rb

@@ -719,7 +719,7 @@ def parse_numeric_instruction
 
       opcode.match(NUMERIC_OPCODE_REGEXP) =>
         { type:, bits:, operation: }
-      type = { 'f' => :float, 'i' => :integer }.fetch(type)
+      type = { 'f' => :float, 'i' => :integer, 'v' => :vector }.fetch(type)
       bits = bits.to_i(10)
 
       case operation
@@ -730,6 +730,8 @@ def parse_numeric_instruction
             parse_integer(bits:)
           in :float
             parse_float(bits:)
+          in :vector
+            parse_vector(bits:)
           end
 
         Const.new(type:, bits:, number:)
@@ -1054,6 +1056,14 @@ def parse_float(bits:)
       Float.parse(read).encode(format:)
     end
 
+    def parse_vector(bits:)
+      raise unless bits == 128
+      read => 'i64x2'
+      read => '0'
+      read => '0'
+      0
+    end
+
     def parse_string
       read => string
       encoding = string.encoding