Remove legacy unknwon/com package (#19298)

Follows: #19284
* The `CopyDir` is only used inside test code
* Rewrite `ToSnakeCase` with more test cases
* The `RedisCacher` only put strings into cache, here we use internal `toStr` to replace the legacy `ToStr`
* The `UniqueQueue` can use string as ID directly, no need to call `ToStr`

modules/util/string_test.go

@@ -0,0 +1,48 @@
+// Copyright 2022 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package util
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestToSnakeCase(t *testing.T) {
+	cases := map[string]string{
+		// all old cases from the legacy package
+		"HTTPServer":         "http_server",
+		"_camelCase":         "_camel_case",
+		"NoHTTPS":            "no_https",
+		"Wi_thF":             "wi_th_f",
+		"_AnotherTES_TCaseP": "_another_tes_t_case_p",
+		"ALL":                "all",
+		"_HELLO_WORLD_":      "_hello_world_",
+		"HELLO_WORLD":        "hello_world",
+		"HELLO____WORLD":     "hello____world",
+		"TW":                 "tw",
+		"_C":                 "_c",
+
+		"  sentence case  ": "__sentence_case__",
+		" Mixed-hyphen case _and SENTENCE_case and UPPER-case": "_mixed_hyphen_case__and_sentence_case_and_upper_case",
+
+		// new cases
+		" ":        "_",
+		"A":        "a",
+		"A0":       "a0",
+		"a0":       "a0",
+		"Aa0":      "aa0",
+		"啊":        "啊",
+		"A啊":       "a啊",
+		"Aa啊b":     "aa啊b",
+		"A啊B":      "a啊_b",
+		"Aa啊B":     "aa啊_b",
+		"TheCase2": "the_case2",
+		"ObjIDs":   "obj_i_ds", // the strange database column name which already exists
+	}
+	for input, expected := range cases {
+		assert.Equal(t, expected, ToSnakeCase(input))
+	}
+}