refactor(rewriter): use custom title case converter implementation instead of golang.org/x/text/cases.Title()

The implementation is equivalent to
`cases.Title(language.English).String(strings.ToLower(…))`,
and this is the only place in miniflux where
"golang.org/x/text/cases" and "golang.org/x/text/language"
are (directly) used.

This reduces the binary size from 27015590 to
26686112 on my machine.

Kudos to https://gsa.zxilly.dev for making it straightforward to catch things
like this.

internal/reader/rewrite/rewrite_functions.go

@@ -11,6 +11,7 @@ import (
 	"net/url"
 	"regexp"
 	"strings"
+	"unicode"
 
 	"miniflux.app/v2/internal/config"
 
@@ -26,6 +27,24 @@ var (
 	textLinkRegex  = regexp.MustCompile(`(?mi)(\bhttps?:\/\/[-A-Z0-9+&@#\/%?=~_|!:,.;]*[-A-Z0-9+&@#\/%=~_|])`)
 )
 
+// titlelize returns a copy of the string s with all Unicode letters that begin words
+// mapped to their Unicode title case.
+func titlelize(s string) string {
+	// A closure is used here to remember the previous character
+	// so that we can check if there is a space preceding the current
+	// character.
+	previous := ' '
+	return strings.Map(
+		func(current rune) rune {
+			if unicode.IsSpace(previous) {
+				previous = current
+				return unicode.ToTitle(current)
+			}
+			previous = current
+			return current
+		}, strings.ToLower(s))
+}
+
 func addImageTitle(entryContent string) string {
 	doc, err := goquery.NewDocumentFromReader(strings.NewReader(entryContent))
 	if err != nil {

internal/reader/rewrite/rewriter.go

@@ -11,9 +11,6 @@ import (
 
 	"miniflux.app/v2/internal/model"
 	"miniflux.app/v2/internal/urllib"
-
-	"golang.org/x/text/cases"
-	"golang.org/x/text/language"
 )
 
 type rule struct {
@@ -94,7 +91,7 @@ func (rule rule) applyRule(entryURL string, entry *model.Entry) {
 	case "remove_tables":
 		entry.Content = removeTables(entry.Content)
 	case "remove_clickbait":
-		entry.Title = cases.Title(language.English).String(strings.ToLower(entry.Title))
+		entry.Title = titlelize(entry.Title)
 	}
 }