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-core/src/main/java/org/springframework/aot/hint/AbstractTypeReference.java

@@ -21,7 +21,7 @@ import java.util.Objects;
 import org.springframework.lang.Nullable;
 
 /**
- * Base {@link TypeReference} implementation that ensures consistent behaviour
+ * Base {@link TypeReference} implementation that ensures consistent behavior
  * for {@code equals()}, {@code hashCode()}, and {@code toString()} based on
  * the {@linkplain #getCanonicalName() canonical name}.
  *

spring-core/src/testFixtures/java/org/springframework/core/testfixture/codec/AbstractDecoderTests.java

@@ -220,7 +220,7 @@ public abstract class AbstractDecoderTests<D extends Decoder<?>> extends Abstrac
 	}
 
 	/**
-	 * Test a {@link Decoder#decode decode} scenario where the input stream is canceled.
+	 * Test a {@link Decoder#decode decode} scenario where the input stream is cancelled.
 	 * This test method will feed the first element of the {@code input} stream to the decoder,
 	 * followed by a cancel signal.
 	 * The result is expected to contain one "normal" element.
@@ -389,7 +389,7 @@ public abstract class AbstractDecoderTests<D extends Decoder<?>> extends Abstrac
 	}
 
 	/**
-	 * Test a {@link Decoder#decodeToMono decode} scenario where the input stream is canceled.
+	 * Test a {@link Decoder#decodeToMono decode} scenario where the input stream is cancelled.
 	 * This test method will immediately cancel the output stream.
 	 *
 	 * @param input the input to be provided to the decoder

spring-core/src/testFixtures/java/org/springframework/core/testfixture/codec/AbstractEncoderTests.java

@@ -187,7 +187,7 @@ public abstract class AbstractEncoderTests<E extends Encoder<?>> extends Abstrac
 	}
 
 	/**
-	 * Test a {@link Encoder#encode encode} scenario where the input stream is canceled.
+	 * Test a {@link Encoder#encode encode} scenario where the input stream is cancelled.
 	 * This test method will feed the first element of the {@code input} stream to the decoder,
 	 * followed by a cancel signal.
 	 * The result is expected to contain one "normal" element.