[experiment] add alternative wasm sqlite3 implementation available via build-tag (#2863)

This allows for building GoToSocial with [SQLite transpiled to WASM](https://github.com/ncruces/go-sqlite3) and accessed through [Wazero](https://wazero.io/).

vendor/github.com/tetratelabs/wazero/internal/wasm/binary/code.go

@@ -0,0 +1,100 @@
+package binary
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"math"
+
+	"github.com/tetratelabs/wazero/internal/leb128"
+	"github.com/tetratelabs/wazero/internal/wasm"
+)
+
+func decodeCode(r *bytes.Reader, codeSectionStart uint64, ret *wasm.Code) (err error) {
+	ss, _, err := leb128.DecodeUint32(r)
+	if err != nil {
+		return fmt.Errorf("get the size of code: %w", err)
+	}
+	remaining := int64(ss)
+
+	// Parse #locals.
+	ls, bytesRead, err := leb128.DecodeUint32(r)
+	remaining -= int64(bytesRead)
+	if err != nil {
+		return fmt.Errorf("get the size locals: %v", err)
+	} else if remaining < 0 {
+		return io.EOF
+	}
+
+	// Validate the locals.
+	bytesRead = 0
+	var sum uint64
+	for i := uint32(0); i < ls; i++ {
+		num, n, err := leb128.DecodeUint32(r)
+		if err != nil {
+			return fmt.Errorf("read n of locals: %v", err)
+		} else if remaining < 0 {
+			return io.EOF
+		}
+
+		sum += uint64(num)
+
+		b, err := r.ReadByte()
+		if err != nil {
+			return fmt.Errorf("read type of local: %v", err)
+		}
+
+		bytesRead += n + 1
+		switch vt := b; vt {
+		case wasm.ValueTypeI32, wasm.ValueTypeF32, wasm.ValueTypeI64, wasm.ValueTypeF64,
+			wasm.ValueTypeFuncref, wasm.ValueTypeExternref, wasm.ValueTypeV128:
+		default:
+			return fmt.Errorf("invalid local type: 0x%x", vt)
+		}
+	}
+
+	if sum > math.MaxUint32 {
+		return fmt.Errorf("too many locals: %d", sum)
+	}
+
+	// Rewind the buffer.
+	_, err = r.Seek(-int64(bytesRead), io.SeekCurrent)
+	if err != nil {
+		return err
+	}
+
+	localTypes := make([]wasm.ValueType, 0, sum)
+	for i := uint32(0); i < ls; i++ {
+		num, bytesRead, err := leb128.DecodeUint32(r)
+		remaining -= int64(bytesRead) + 1 // +1 for the subsequent ReadByte
+		if err != nil {
+			return fmt.Errorf("read n of locals: %v", err)
+		} else if remaining < 0 {
+			return io.EOF
+		}
+
+		b, err := r.ReadByte()
+		if err != nil {
+			return fmt.Errorf("read type of local: %v", err)
+		}
+
+		for j := uint32(0); j < num; j++ {
+			localTypes = append(localTypes, b)
+		}
+	}
+
+	bodyOffsetInCodeSection := codeSectionStart - uint64(r.Len())
+	body := make([]byte, remaining)
+	if _, err = io.ReadFull(r, body); err != nil {
+		return fmt.Errorf("read body: %w", err)
+	}
+
+	if endIndex := len(body) - 1; endIndex < 0 || body[endIndex] != wasm.OpcodeEnd {
+		return fmt.Errorf("expr not end with OpcodeEnd")
+	}
+
+	ret.BodyOffsetInCodeSection = bodyOffsetInCodeSection
+	ret.LocalTypes = localTypes
+	ret.Body = body
+	return nil
+}