Consistently use American English spelling

Since the Spring Framework uses American English spelling, this commit
updates Javadoc and the reference manual to ensure consistency in that
regard. However, there are two exceptions to this rule that arise due
to their use within a technical context.

- We use "cancelled/cancelling" instead of "canceled/canceling" in
  numerous places (including error messages).
- We use "implementor" instead of "implementer".

Closes gh-36470

(cherry picked from commit 17699103dc)

spring-expression/src/test/java/org/springframework/expression/spel/ExpressionLanguageScenarioTests.java

@@ -243,7 +243,7 @@ class ExpressionLanguageScenarioTests extends AbstractExpressionTests {
 
 
 	/**
-	 * Regardless of the current context object, or root context object, this resolver can tell you what colour a fruit is !
+	 * Regardless of the current context object, or root context object, this resolver can tell you what color a fruit is !
 	 * It only supports property reading, not writing.  To support writing it would need to override canWrite() and write()
 	 */
 	private static class FruitColourAccessor implements PropertyAccessor {
@@ -284,7 +284,7 @@ class ExpressionLanguageScenarioTests extends AbstractExpressionTests {
 
 
 	/**
-	 * Regardless of the current context object, or root context object, this resolver can tell you what colour a vegetable is !
+	 * Regardless of the current context object, or root context object, this resolver can tell you what color a vegetable is !
 	 * It only supports property reading, not writing.
 	 */
 	private static class VegetableColourAccessor implements PropertyAccessor {