Flattens Memory and Table types and backfills Table encoder (#356)

This flattens Memory and Table types, particularly making it a
compilation error to add multiple of either.

This also backfills binary encoding of Table.

Signed-off-by: Adrian Cole <adrian@tetrate.io>

internal/wasm/binary/table.go

@@ -0,0 +1,45 @@
+package binary
+
+import (
+	"bytes"
+	"fmt"
+
+	wasm "github.com/tetratelabs/wazero/internal/wasm"
+)
+
+// decodeTable returns the wasm.Table decoded with the WebAssembly 1.0 (20191205) Binary Format.
+//
+// See https://www.w3.org/TR/2019/REC-wasm-core-1-20191205/#binary-table
+func decodeTable(r *bytes.Reader) (*wasm.Table, error) {
+	b, err := r.ReadByte()
+	if err != nil {
+		return nil, fmt.Errorf("read leading byte: %v", err)
+	}
+
+	if b != wasm.ElemTypeFuncref {
+		return nil, fmt.Errorf("invalid element type %#x != funcref(%#x)", b, wasm.ElemTypeFuncref)
+	}
+
+	min, max, err := decodeLimitsType(r)
+	if err != nil {
+		return nil, fmt.Errorf("read limits: %v", err)
+	}
+	if min > wasm.MaximumFunctionIndex {
+		return nil, fmt.Errorf("table min must be at most %d", wasm.MaximumFunctionIndex)
+	}
+	if max != nil {
+		if *max < min {
+			return nil, fmt.Errorf("table size minimum must not be greater than maximum")
+		} else if *max > wasm.MaximumFunctionIndex {
+			return nil, fmt.Errorf("table max must be at most %d", wasm.MaximumFunctionIndex)
+		}
+	}
+	return &wasm.Table{Min: min, Max: max}, nil
+}
+
+// encodeTable returns the internalwasm.Table encoded in WebAssembly 1.0 (20191205) Binary Format.
+//
+// See https://www.w3.org/TR/2019/REC-wasm-core-1-20191205/#binary-table
+func encodeTable(i *wasm.Table) []byte {
+	return append([]byte{wasm.ElemTypeFuncref}, encodeLimitsType(i.Min, i.Max)...)
+}