Extract source api from app module (#8014)

* Extract source api from app module

* Extract source online api from app module

(cherry picked from commit 86fe850794)

# Conflicts:
#	app/src/main/java/eu/kanade/tachiyomi/data/backup/BackupManager.kt
#	core/src/main/java/eu/kanade/tachiyomi/network/NetworkHelper.kt
#	source-api/src/main/java/eu/kanade/tachiyomi/source/Source.kt
#	source-api/src/main/java/eu/kanade/tachiyomi/source/model/SManga.kt

core/src/main/java/exh/util/ListUtil.kt

@@ -0,0 +1,3 @@
+package exh.util
+
+fun <C : Collection<R>, R> C.nullIfEmpty() = ifEmpty { null }

core/src/main/java/exh/util/StringBuilderExtensions.kt

@@ -0,0 +1,3 @@
+package exh.util
+
+operator fun StringBuilder.plusAssign(other: String) { append(other) }

core/src/main/java/exh/util/StringUtil.kt

@@ -0,0 +1,20 @@
+package exh.util
+
+import java.util.Locale
+
+fun Collection<String>.trimAll() = map { it.trim() }
+fun Collection<String>.dropBlank() = filter { it.isNotBlank() }
+fun Collection<String>.dropEmpty() = filter { it.isNotEmpty() }
+
+private val articleRegex by lazy { "^(an|a|the) ".toRegex(RegexOption.IGNORE_CASE) }
+
+fun String.removeArticles(): String {
+    return replace(articleRegex, "")
+}
+
+fun String.trimOrNull() = trim().nullIfBlank()
+
+fun String.nullIfBlank(): String? = ifBlank { null }
+
+fun String.capitalize(locale: Locale = Locale.getDefault()) =
+    replaceFirstChar { if (it.isLowerCase()) it.titlecase(locale) else it.toString() }