Refactor INI package (first step) (#25024)

The INI package has many bugs and quirks, and in fact it is
unmaintained.

This PR is the first step for the INI package refactoring: 

* Use Gitea's "config_provider" to provide INI access
* Deprecate the INI package by golangci.yml rule

modules/setting/config_provider_test.go

@@ -4,6 +4,7 @@
 package setting
 
 import (
+	"os"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -64,3 +65,57 @@ key = 123
 	assert.Equal(t, "", ConfigSectionKeyString(sec, "empty"))
 	assert.Equal(t, "def", ConfigSectionKeyString(secSub, "empty"))
 }
+
+func TestNewConfigProviderFromFile(t *testing.T) {
+	_, err := NewConfigProviderFromFile(&Options{CustomConf: "no-such.ini", AllowEmpty: false})
+	assert.ErrorContains(t, err, "unable to find configuration file")
+
+	// load non-existing file and save
+	testFile := t.TempDir() + "/test.ini"
+	testFile1 := t.TempDir() + "/test1.ini"
+	cfg, err := NewConfigProviderFromFile(&Options{CustomConf: testFile, AllowEmpty: true})
+	assert.NoError(t, err)
+
+	sec, _ := cfg.NewSection("foo")
+	_, _ = sec.NewKey("k1", "a")
+	assert.NoError(t, cfg.Save())
+	_, _ = sec.NewKey("k2", "b")
+	assert.NoError(t, cfg.SaveTo(testFile1))
+
+	bs, err := os.ReadFile(testFile)
+	assert.NoError(t, err)
+	assert.Equal(t, "[foo]\nk1=a\n", string(bs))
+
+	bs, err = os.ReadFile(testFile1)
+	assert.NoError(t, err)
+	assert.Equal(t, "[foo]\nk1=a\nk2=b\n", string(bs))
+
+	// load existing file and save
+	cfg, err = NewConfigProviderFromFile(&Options{CustomConf: testFile, AllowEmpty: true})
+	assert.NoError(t, err)
+	assert.Equal(t, "a", cfg.Section("foo").Key("k1").String())
+	sec, _ = cfg.NewSection("bar")
+	_, _ = sec.NewKey("k1", "b")
+	assert.NoError(t, cfg.Save())
+	bs, err = os.ReadFile(testFile)
+	assert.NoError(t, err)
+	assert.Equal(t, "[foo]\nk1=a\n\n[bar]\nk1=b\n", string(bs))
+}
+
+func TestNewConfigProviderForLocale(t *testing.T) {
+	// load locale from file
+	localeFile := t.TempDir() + "/locale.ini"
+	_ = os.WriteFile(localeFile, []byte(`k1=a`), 0o644)
+	cfg, err := NewConfigProviderForLocale(localeFile)
+	assert.NoError(t, err)
+	assert.Equal(t, "a", cfg.Section("").Key("k1").String())
+
+	// load locale from bytes
+	cfg, err = NewConfigProviderForLocale([]byte("k1=foo\nk2=bar"))
+	assert.NoError(t, err)
+	assert.Equal(t, "foo", cfg.Section("").Key("k1").String())
+	cfg, err = NewConfigProviderForLocale([]byte("k1=foo\nk2=bar"), []byte("k2=xxx"))
+	assert.NoError(t, err)
+	assert.Equal(t, "foo", cfg.Section("").Key("k1").String())
+	assert.Equal(t, "xxx", cfg.Section("").Key("k2").String())
+}