[db] Add SearchQueryRewriter and use it in AppSearchItemsTest

This code comes from SearchManager, but making it available in the DB library makes sense since the queries are specific to the DB implementation such as zero-whitespace hack.

libs/database/src/test/java/org/fdroid/database/SearchQueryRewriterTest.kt

@@ -0,0 +1,54 @@
+package org.fdroid.database
+
+import kotlin.test.assertEquals
+import org.junit.Test
+
+internal class SearchQueryRewriterTest {
+
+  @Test
+  fun rewritesBlankQueryToBlank() {
+    assertEquals("", SearchQueryRewriter.rewriteQuery("   "))
+  }
+
+  @Test
+  fun rewritesSingleLatinWordToPrefixQuery() {
+    assertEquals("foo*", SearchQueryRewriter.rewriteQuery("foo"))
+  }
+
+  @Test
+  fun rewritesMultipleLatinWordsWithCamelCaseAndPhrase() {
+    assertEquals(
+      "foo* bar* OR foobar* OR \"foo* bar*\"",
+      SearchQueryRewriter.rewriteQuery("foo bar"),
+    )
+  }
+
+  @Test
+  fun rewritesMultipleLatinWordsAndIgnoresExtraWhitespace() {
+    assertEquals(
+      "foo* bar* OR foobar* OR \"foo* bar*\"",
+      SearchQueryRewriter.rewriteQuery("  foo   bar  "),
+    )
+  }
+
+  @Test
+  fun rewritesSingleCjkWordWithZeroWidthAndVerbatimAlternatives() {
+    assertEquals("測* 試* OR \"測\u200B試*\" OR 測試*", SearchQueryRewriter.rewriteQuery("測試"))
+  }
+
+  @Test
+  fun rewritesMultiWordCjkQuery() {
+    assertEquals(
+      "測* 試* 艾* 星* OR \"測\u200B試*\" \"艾\u200B星*\" OR 測試* 艾星*",
+      SearchQueryRewriter.rewriteQuery("測試 艾星"),
+    )
+  }
+
+  @Test
+  fun rewritesMixedLatinAndCjkWordsUsingCjkBranch() {
+    assertEquals(
+      "foo* 測* 試* OR \"foo*\" \"測\u200B試*\" OR foo* 測試*",
+      SearchQueryRewriter.rewriteQuery("foo 測試"),
+    )
+  }
+}