Make AbstractCapabilities.asMap return Map<String, Object>

Co-variant return types mean that this is legal to do in Java,
and it makes dealing with the output of these things easier.

With hindsight, it would have been better to use a different
return type for `asMap` in the first place. Maybe we can fix
this in Selenium 4.

java/client/src/org/openqa/selenium/AbstractCapabilities.java

@@ -98,7 +98,7 @@ protected void setCapability(String key, Object value) {
   }
 
   @Override
-  public Map<String, ?> asMap() {
+  public Map<String, Object> asMap() {
     return Collections.unmodifiableMap(caps);
   }
 

java/client/src/org/openqa/selenium/chrome/ChromeOptions.java

@@ -272,7 +272,7 @@ protected int amendHashCode() {
   }
 
   @Override
-  public Map<String, ?> asMap() {
+  public Map<String, Object> asMap() {
     Map<String, Object> toReturn = new TreeMap<>();
     toReturn.putAll(super.asMap());
 

java/client/src/org/openqa/selenium/edge/EdgeOptions.java

@@ -94,7 +94,7 @@ MutableCapabilities toCapabilities() {
   }
 
   @Override
-  public Map<String, ?> asMap() {
+  public Map<String, Object> asMap() {
     return ImmutableMap.of(CAPABILITY, super.asMap());
   }
 }

java/client/src/org/openqa/selenium/firefox/FirefoxOptions.java

@@ -338,7 +338,7 @@ public void setCapability(String key, Object value) {
   }
 
   @Override
-  public Map<String, ?> asMap() {
+  public Map<String, Object> asMap() {
     TreeMap<String, Object> toReturn = new TreeMap<>();
     toReturn.putAll(super.asMap());
 

java/client/src/org/openqa/selenium/opera/OperaOptions.java

@@ -207,7 +207,7 @@ public OperaOptions setProxy(Proxy proxy) {
   }
 
   @Override
-  public Map<String, ?> asMap() {
+  public Map<String, Object> asMap() {
     Map<String, Object> toReturn = new TreeMap<>();
     toReturn.putAll(super.asMap());
 

java/client/src/org/openqa/selenium/safari/SafariOptions.java

@@ -257,7 +257,7 @@ protected int amendHashCode() {
   }
 
   @Override
-  public Map<String, ?> asMap() {
+  public Map<String, Object> asMap() {
     return ImmutableSortedMap.<String, Object>naturalOrder()
         .putAll(super.asMap())
         .put(CAPABILITY, options)