bake: update ReadRemoteFiles to use buildkit api

Signed-off-by: Justin Chadwell <me@jedevc.com>

vendor/github.com/moby/buildkit/frontend/dockerfile/dockerignore/dockerignore.go

@@ -0,0 +1,65 @@
+package dockerignore
+
+import (
+	"bufio"
+	"bytes"
+	"io"
+	"path/filepath"
+	"strings"
+
+	"github.com/pkg/errors"
+)
+
+// ReadAll reads a .dockerignore file and returns the list of file patterns
+// to ignore. Note this will trim whitespace from each line as well
+// as use GO's "clean" func to get the shortest/cleanest path for each.
+func ReadAll(reader io.Reader) ([]string, error) {
+	if reader == nil {
+		return nil, nil
+	}
+
+	scanner := bufio.NewScanner(reader)
+	var excludes []string
+	currentLine := 0
+
+	utf8bom := []byte{0xEF, 0xBB, 0xBF}
+	for scanner.Scan() {
+		scannedBytes := scanner.Bytes()
+		// We trim UTF8 BOM
+		if currentLine == 0 {
+			scannedBytes = bytes.TrimPrefix(scannedBytes, utf8bom)
+		}
+		pattern := string(scannedBytes)
+		currentLine++
+		// Lines starting with # (comments) are ignored before processing
+		if strings.HasPrefix(pattern, "#") {
+			continue
+		}
+		pattern = strings.TrimSpace(pattern)
+		if pattern == "" {
+			continue
+		}
+		// normalize absolute paths to paths relative to the context
+		// (taking care of '!' prefix)
+		invert := pattern[0] == '!'
+		if invert {
+			pattern = strings.TrimSpace(pattern[1:])
+		}
+		if len(pattern) > 0 {
+			pattern = filepath.Clean(pattern)
+			pattern = filepath.ToSlash(pattern)
+			if len(pattern) > 1 && pattern[0] == '/' {
+				pattern = pattern[1:]
+			}
+		}
+		if invert {
+			pattern = "!" + pattern
+		}
+
+		excludes = append(excludes, pattern)
+	}
+	if err := scanner.Err(); err != nil {
+		return nil, errors.Wrap(err, "error reading .dockerignore")
+	}
+	return excludes, nil
+}