[nus-cs2103-AY2122S1#319] Checkstyle: enforce separators' placement in line wraps (#368)

Our coding standard for Java requires separators' placement in line
wraps to follow specific rules, such as having comma (,) stay attached
to the token that precedes it and having the dot (.) in a new line.
These rules are not enforced by checkstyle.

Let's teach Checkstyle to be stricter about line wrapping around some 
symbols by adding the relevant SeparatorWrap rules.

Author: eugenepeh

config/checkstyle/checkstyle.xml

@@ -322,6 +322,17 @@
       <property name="message" value="Trailing whitespace"/>
     </module>
 
+    <module name="SeparatorWrap">
+      <!-- Checks that the ".", "@" is at the next line in a line wrap. -->
+      <property name="tokens" value="DOT, AT"/>
+      <property name="option" value="nl"/>
+    </module>
+    <module name="SeparatorWrap">
+      <!-- Checks that the ",", "]", "[", "...", ";", "(" is at the previous end of line in a line wrap. -->
+      <property name="tokens" value="COMMA, RBRACK, ARRAY_DECLARATOR, ELLIPSIS, SEMI, LPAREN"/>
+      <property name="option" value="eol"/>
+    </module>
+
     <module name="Indentation">
       <property name="caseIndent" value="0" />
     </module>

src/main/java/seedu/address/model/person/UniquePersonList.java

@@ -103,8 +103,7 @@ public Iterator<Person> iterator() {
     public boolean equals(Object other) {
         return other == this // short circuit if same object
                 || (other instanceof UniquePersonList // instanceof handles nulls
-                && this.internalList.equals(
-                ((UniquePersonList) other).internalList));
+                        && this.internalList.equals(((UniquePersonList) other).internalList));
     }
 
     @Override

src/main/java/seedu/address/model/tag/UniqueTagList.java

@@ -150,8 +150,7 @@ public UnmodifiableObservableList<Tag> asObservableList() {
     public boolean equals(Object other) {
         return other == this // short circuit if same object
                 || (other instanceof UniqueTagList // instanceof handles nulls
-                && this.internalList.equals(
-                ((UniqueTagList) other).internalList));
+                        && this.internalList.equals(((UniqueTagList) other).internalList));
     }
 
     public boolean equalsOrderInsensitive(UniqueTagList other) {

src/test/java/seedu/address/ui/TestFxmlObject.java

@@ -27,8 +27,8 @@ public void setText(String text) {
 
     @Override
     public boolean equals(Object other) {
-        return other == this ||
-                (other instanceof TestFxmlObject
+        return other == this // short circuit if same object
+                || (other instanceof TestFxmlObject // instanceof handles nulls
                         && this.text.equals(((TestFxmlObject) other).getText()));
     }