Add signature test to Servlet TCK

[markt-asf]

Machinery copied from EL with some code clean up (warnings fixed, unused code removed, added generics).
Tested with Tomcat that has it's own Servlet API JAR and found a Tomcat bug that has since been fixed.

[olamy]

@markt-asf LGTM but you need to change the file .github/workflows/maven.yml to use jdk17.

diff --git a/.github/workflows/maven.yml b/.github/workflows/maven.yml
index fc541a5..6c3ca89 100644
--- a/.github/workflows/maven.yml
+++ b/.github/workflows/maven.yml
@@ -8,11 +8,13 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-    - uses: actions/checkout@v1
-    - name: Set up JDK 11
-      uses: actions/setup-java@v1
+    - uses: actions/checkout@v4
+    - name: Set up JDK 17
+      uses: actions/setup-java@v3
       with:
-        java-version: 11
+        java-version: 17
+        distribution: temurin
+        cache: 'maven'
     - name: Set up Maven
       run:
         mvn --errors --batch-mode --show-version org.apache.maven.plugins:maven-wrapper-plugin:3.2.0:wrapper "-Dmaven=3.9.4"

I will propose to use dependabot in another PR to have some auto PRs to upgrade this.

[markt-asf]

Tx for the review. I'll make that change and then merge.