Use new String APIs in place of util apis of Strings.* package (#2675)

- This change is only for some metadata/ apis only.
- Bumped up java version for this.
More details in cl/396604897

metadata/pom.xml

@@ -43,8 +43,8 @@
         <artifactId>maven-compiler-plugin</artifactId>
         <version>3.8.1</version>
         <configuration>
-          <source>8</source>
-          <target>8</target>
+          <source>11</source>
+          <target>11</target>
         </configuration>
         <executions>
           <execution>

metadata/src/main/java/com/google/i18n/phonenumbers/metadata/model/FormatSpec.java

@@ -20,7 +20,6 @@ import static com.google.common.base.Preconditions.checkState;
 
 import com.google.auto.value.AutoValue;
 import com.google.common.base.CharMatcher;
-import com.google.common.base.Strings;
 import com.google.common.collect.ImmutableList;
 import com.google.i18n.phonenumbers.metadata.RangeSpecification;
 import com.google.i18n.phonenumbers.metadata.RangeTree;
@@ -621,7 +620,7 @@ public abstract class FormatSpec {
     @Override
     public final String toString() {
       String group =
-          Strings.repeat("X", minLength()) + Strings.repeat("*", maxLength() - minLength());
+          "X".repeat(minLength()) + "*".repeat(maxLength() - minLength());
       return replacement().map(r -> String.format("{%s>%s}", group, r)).orElse(group);
     }
   }

metadata/src/test/java/com/google/i18n/phonenumbers/metadata/RangeTreeTest.java

@@ -18,12 +18,11 @@ package com.google.i18n.phonenumbers.metadata;
 import static com.google.common.collect.ImmutableList.toImmutableList;
 import static com.google.common.truth.Truth.assertThat;
 import static com.google.i18n.phonenumbers.metadata.DigitSequence.domain;
+import static com.google.i18n.phonenumbers.metadata.testing.AssertUtil.assertThrows;
 import static com.google.i18n.phonenumbers.metadata.testing.RangeTreeSubject.assertThat;
 import static java.util.Arrays.asList;
-import static com.google.i18n.phonenumbers.metadata.testing.AssertUtil.assertThrows;
 
 import com.google.auto.value.AutoValue;
-import com.google.common.base.Strings;
 import com.google.common.collect.ImmutableRangeSet;
 import com.google.common.collect.Range;
 import com.google.common.collect.RangeSet;
@@ -505,7 +504,7 @@ public class RangeTreeTest {
     RangeTree combined = new ForkJoinPool(numThreads)
         .submit(() -> ranges.parallelStream().reduce(RangeTree.empty(), RangeTree::union))
         .get();
-    assertThat(combined).isEqualTo(ranges(Strings.repeat("x", numDigits)));
+    assertThat(combined).isEqualTo(ranges("x".repeat(numDigits)));
   }
 
   @AutoValue