[CHORE] Drop go-git support

See https://codeberg.org/forgejo/discussions/issues/164 for the
rationale and discussion of this change.

Everything related to the `go-git` dependency is dropped (Only a single
instance is left in a test file to test for an XSS, it requires crafting
an commit that Git itself refuses to craft). `_gogit` files have
been removed entirely, `go:build: !gogit` is removed, `XXX_nogogit.go` files
either have been renamed or had their code being merged into the
`XXX.go` file.

modules/git/repo_ref.go

@@ -4,8 +4,10 @@
 package git
 
 import (
+	"bufio"
 	"context"
 	"fmt"
+	"io"
 	"strings"
 
 	"code.gitea.io/gitea/modules/util"
@@ -78,3 +80,78 @@ func (repo *Repository) ExpandRef(ref string) (string, error) {
 	}
 	return "", fmt.Errorf("could not expand reference '%s'", ref)
 }
+
+// GetRefsFiltered returns all references of the repository that matches patterm exactly or starting with.
+func (repo *Repository) GetRefsFiltered(pattern string) ([]*Reference, error) {
+	stdoutReader, stdoutWriter := io.Pipe()
+	defer func() {
+		_ = stdoutReader.Close()
+		_ = stdoutWriter.Close()
+	}()
+
+	go func() {
+		stderrBuilder := &strings.Builder{}
+		err := NewCommand(repo.Ctx, "for-each-ref").Run(&RunOpts{
+			Dir:    repo.Path,
+			Stdout: stdoutWriter,
+			Stderr: stderrBuilder,
+		})
+		if err != nil {
+			_ = stdoutWriter.CloseWithError(ConcatenateError(err, stderrBuilder.String()))
+		} else {
+			_ = stdoutWriter.Close()
+		}
+	}()
+
+	refs := make([]*Reference, 0)
+	bufReader := bufio.NewReader(stdoutReader)
+	for {
+		// The output of for-each-ref is simply a list:
+		// <sha> SP <type> TAB <ref> LF
+		sha, err := bufReader.ReadString(' ')
+		if err == io.EOF {
+			break
+		}
+		if err != nil {
+			return nil, err
+		}
+		sha = sha[:len(sha)-1]
+
+		typ, err := bufReader.ReadString('\t')
+		if err == io.EOF {
+			// This should not happen, but we'll tolerate it
+			break
+		}
+		if err != nil {
+			return nil, err
+		}
+		typ = typ[:len(typ)-1]
+
+		refName, err := bufReader.ReadString('\n')
+		if err == io.EOF {
+			// This should not happen, but we'll tolerate it
+			break
+		}
+		if err != nil {
+			return nil, err
+		}
+		refName = refName[:len(refName)-1]
+
+		// refName cannot be HEAD but can be remotes or stash
+		if strings.HasPrefix(refName, RemotePrefix) || refName == "/refs/stash" {
+			continue
+		}
+
+		if pattern == "" || strings.HasPrefix(refName, pattern) {
+			r := &Reference{
+				Name:   refName,
+				Object: MustIDFromString(sha),
+				Type:   typ,
+				repo:   repo,
+			}
+			refs = append(refs, r)
+		}
+	}
+
+	return refs, nil
+}