Bump checkstyle from 6.17 to 8.18

Bumps [checkstyle](https://github.com/checkstyle/checkstyle) from 6.17 to 8.18.
- [Release notes](https://github.com/checkstyle/checkstyle/releases)
- [Commits](checkstyle/checkstyle@checkstyle-6.17...checkstyle-8.18)

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

build-tools/src/main/resources/checkstyle/tmc-checkstyle.xml

@@ -56,9 +56,6 @@
             <property name="tokens" value="LITERAL_TRY, LITERAL_FINALLY, LITERAL_IF, LITERAL_ELSE, LITERAL_SWITCH"/>
         </module>
         <module name="NeedBraces"/>
-        <module name="LeftCurly">
-            <property name="maxLineLength" value="100"/>
-        </module>
         <module name="RightCurly"/>
         <module name="RightCurly">
             <property name="option" value="alone"/>
@@ -153,12 +150,6 @@
         </module>
         <module name="OverloadMethodsDeclarationOrder"/>
         <module name="VariableDeclarationUsageDistance"/>
-        <module name="CustomImportOrder">
-            <property name="thirdPartyPackageRegExp" value=".*"/>
-            <property name="specialImportsRegExp" value="^fi.helsinki"/>
-            <property name="sortImportsInGroupAlphabetically" value="true"/>
-            <property name="customImportOrderRules" value="STATIC###SPECIAL_IMPORTS###THIRD_PARTY_PACKAGE###STANDARD_JAVA_PACKAGE"/>
-        </module>
         <module name="MethodParamPad"/>
         <module name="OperatorWrap">
             <property name="option" value="NL"/>

pom.xml

@@ -53,7 +53,7 @@
         <dependency>
             <groupId>com.puppycrawl.tools</groupId>
             <artifactId>checkstyle</artifactId>
-            <version>6.17</version>
+            <version>8.18</version>
         </dependency>
 
         <dependency>
@@ -113,12 +113,12 @@
                 <plugin>
                     <groupId>org.apache.maven.plugins</groupId>
                     <artifactId>maven-checkstyle-plugin</artifactId>
-                    <version>2.16</version>
+                    <version>3.1.0</version>
                     <dependencies>
                         <dependency>
                             <groupId>com.puppycrawl.tools</groupId>
                             <artifactId>checkstyle</artifactId>
-                            <version>6.17</version>
+                            <version>8.18</version>
                         </dependency>
                     </dependencies>
                 </plugin>
@@ -129,7 +129,7 @@
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-checkstyle-plugin</artifactId>
-                <version>2.15</version>
+                <version>3.1.0</version>
                 <inherited>true</inherited>
                 <dependencies>
                     <dependency>