Refactor Git Attribute & performance optimization (#34154)

This PR moved git attributes related code to `modules/git/attribute` sub
package and moved language stats related code to
`modules/git/languagestats` sub package to make it easier to maintain.

And it also introduced a performance improvement which use the `git
check-attr --source` which can be run in a bare git repository so that
we don't need to create a git index file. The new parameter need a git
version >= 2.40 . If git version less than 2.40, it will fall back to
previous implementation.

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: yp05327 <576951401@qq.com>

modules/git/attribute/attribute.go

@@ -0,0 +1,114 @@
+// Copyright 2025 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package attribute
+
+import (
+	"strings"
+
+	"code.gitea.io/gitea/modules/optional"
+)
+
+type Attribute string
+
+const (
+	LinguistVendored      = "linguist-vendored"
+	LinguistGenerated     = "linguist-generated"
+	LinguistDocumentation = "linguist-documentation"
+	LinguistDetectable    = "linguist-detectable"
+	LinguistLanguage      = "linguist-language"
+	GitlabLanguage        = "gitlab-language"
+	Lockable              = "lockable"
+	Filter                = "filter"
+)
+
+var LinguistAttributes = []string{
+	LinguistVendored,
+	LinguistGenerated,
+	LinguistDocumentation,
+	LinguistDetectable,
+	LinguistLanguage,
+	GitlabLanguage,
+}
+
+func (a Attribute) IsUnspecified() bool {
+	return a == "" || a == "unspecified"
+}
+
+func (a Attribute) ToString() optional.Option[string] {
+	if !a.IsUnspecified() {
+		return optional.Some(string(a))
+	}
+	return optional.None[string]()
+}
+
+// ToBool converts the attribute value to optional boolean: true if "set"/"true", false if "unset"/"false", none otherwise
+func (a Attribute) ToBool() optional.Option[bool] {
+	switch a {
+	case "set", "true":
+		return optional.Some(true)
+	case "unset", "false":
+		return optional.Some(false)
+	}
+	return optional.None[bool]()
+}
+
+type Attributes struct {
+	m map[string]Attribute
+}
+
+func NewAttributes() *Attributes {
+	return &Attributes{m: make(map[string]Attribute)}
+}
+
+func (attrs *Attributes) Get(name string) Attribute {
+	if value, has := attrs.m[name]; has {
+		return value
+	}
+	return ""
+}
+
+func (attrs *Attributes) GetVendored() optional.Option[bool] {
+	return attrs.Get(LinguistVendored).ToBool()
+}
+
+func (attrs *Attributes) GetGenerated() optional.Option[bool] {
+	return attrs.Get(LinguistGenerated).ToBool()
+}
+
+func (attrs *Attributes) GetDocumentation() optional.Option[bool] {
+	return attrs.Get(LinguistDocumentation).ToBool()
+}
+
+func (attrs *Attributes) GetDetectable() optional.Option[bool] {
+	return attrs.Get(LinguistDetectable).ToBool()
+}
+
+func (attrs *Attributes) GetLinguistLanguage() optional.Option[string] {
+	return attrs.Get(LinguistLanguage).ToString()
+}
+
+func (attrs *Attributes) GetGitlabLanguage() optional.Option[string] {
+	attrStr := attrs.Get(GitlabLanguage).ToString()
+	if attrStr.Has() {
+		raw := attrStr.Value()
+		// gitlab-language may have additional parameters after the language
+		// ignore them and just use the main language
+		// https://docs.gitlab.com/ee/user/project/highlighting.html#override-syntax-highlighting-for-a-file-type
+		if idx := strings.IndexByte(raw, '?'); idx >= 0 {
+			return optional.Some(raw[:idx])
+		}
+	}
+	return attrStr
+}
+
+func (attrs *Attributes) GetLanguage() optional.Option[string] {
+	// prefer linguist-language over gitlab-language
+	// if linguist-language is not set, use gitlab-language
+	// if both are not set, return none
+	language := attrs.GetLinguistLanguage()
+	if language.Value() == "" {
+		language = attrs.GetGitlabLanguage()
+	}
+	return language
+}