Move IsReadmeFile* from modules/markup/ to modules/util (#22877)

These functions don't examine contents, just filenames, so they don't
fit in well in a markup module.

This was originally part of
https://github.com/go-gitea/gitea/pull/22177.

Signed-off-by: Nick Guenther <nick.guenther@polymtl.ca>

modules/markup/renderer_test.go

@@ -2,94 +2,3 @@
 // SPDX-License-Identifier: MIT
 
 package markup_test
-
-import (
-	"testing"
-
-	. "code.gitea.io/gitea/modules/markup"
-
-	_ "code.gitea.io/gitea/modules/markup/markdown"
-
-	"github.com/stretchr/testify/assert"
-)
-
-func TestMisc_IsReadmeFile(t *testing.T) {
-	trueTestCases := []string{
-		"readme",
-		"README",
-		"readME.mdown",
-		"README.md",
-		"readme.i18n.md",
-	}
-	falseTestCases := []string{
-		"test.md",
-		"wow.MARKDOWN",
-		"LOL.mDoWn",
-		"test",
-		"abcdefg",
-		"abcdefghijklmnopqrstuvwxyz",
-		"test.md.test",
-		"readmf",
-	}
-
-	for _, testCase := range trueTestCases {
-		assert.True(t, IsReadmeFile(testCase))
-	}
-	for _, testCase := range falseTestCases {
-		assert.False(t, IsReadmeFile(testCase))
-	}
-
-	type extensionTestcase struct {
-		name     string
-		expected bool
-		idx      int
-	}
-
-	exts := []string{".md", ".txt", ""}
-	testCasesExtensions := []extensionTestcase{
-		{
-			name:     "readme",
-			expected: true,
-			idx:      2,
-		},
-		{
-			name:     "readme.md",
-			expected: true,
-			idx:      0,
-		},
-		{
-			name:     "README.md",
-			expected: true,
-			idx:      0,
-		},
-		{
-			name:     "ReAdMe.Md",
-			expected: true,
-			idx:      0,
-		},
-		{
-			name:     "readme.txt",
-			expected: true,
-			idx:      1,
-		},
-		{
-			name:     "readme.doc",
-			expected: true,
-			idx:      3,
-		},
-		{
-			name: "readmee.md",
-		},
-		{
-			name:     "readme..",
-			expected: true,
-			idx:      3,
-		},
-	}
-
-	for _, testCase := range testCasesExtensions {
-		idx, ok := IsReadmeFileExtension(testCase.name, exts...)
-		assert.Equal(t, testCase.expected, ok)
-		assert.Equal(t, testCase.idx, idx)
-	}
-}