Revise SpEL inline collection caching improvements

This commit revises the contribution for gh-25921 in the following ways.

- Use instanceof pattern matching

- Use List.of() and Map.of()

- Add missing @⁠since tags

- Polish Javadoc

- Rename isNegativeNumber() to isNegativeNumberLiteral()

- Restructure InlineCollectionTests using @⁠Nested, etc.

- Fix testListWithVariableNotCached() test: it previously set a SpEL
  "variable" but tested a "property" in the root context object, which
  effectively did not test anything.

- Introduce additional tests: listWithPropertyAccessIsNotCached(),
  mapWithVariableIsNotCached(), and mapWithPropertyAccessIsNotCached().

Author: sbrannen

spring-expression/src/main/java/org/springframework/expression/spel/ast/InlineList.java

@@ -68,7 +68,7 @@ private TypedValue computeConstantValue() {
 						return null;
 					}
 				}
-				else if (!(child instanceof OpMinus) || !((OpMinus) child).isNegativeNumber()) {
+				else if (!(child instanceof OpMinus opMinus) || !opMinus.isNegativeNumberLiteral()) {
 					return null;
 				}
 			}

spring-expression/src/main/java/org/springframework/expression/spel/ast/InlineMap.java

@@ -71,7 +71,7 @@ else if (child instanceof InlineMap inlineMap) {
 					}
 				}
 				else if (!(c % 2 == 0 && child instanceof PropertyOrFieldReference)) {
-					if (!(child instanceof OpMinus) || !((OpMinus) child).isNegativeNumber()) {
+					if (!(child instanceof OpMinus opMinus) || !opMinus.isNegativeNumberLiteral()) {
 						return null;
 					}
 				}

spring-expression/src/main/java/org/springframework/expression/spel/ast/Literal.java

@@ -53,6 +53,18 @@ public final TypedValue getValueInternal(ExpressionState state) throws SpelEvalu
 		return getLiteralValue();
 	}
 
+	/**
+	 * Determine if this literal represents a number.
+	 * @return {@code true} if this literal represents a number
+	 * @since 6.1
+	 */
+	public boolean isNumberLiteral() {
+		return (this instanceof IntLiteral ||
+				this instanceof LongLiteral ||
+				this instanceof FloatLiteral ||
+				this instanceof RealLiteral);
+	}
+
 	@Override
 	public String toString() {
 		return String.valueOf(getLiteralValue().getValue());
@@ -111,15 +123,4 @@ public static Literal getRealLiteral(String numberToken, int startPos, int endPo
 		}
 	}
 
-	/**
-	 * Check whether this literal is a number.
-	 * @return true if this is a number
-	 */
-	public boolean isNumberLiteral() {
-		return this instanceof IntLiteral ||
-				this instanceof LongLiteral ||
-				this instanceof FloatLiteral ||
-				this instanceof RealLiteral;
-	}
-
 }

spring-expression/src/main/java/org/springframework/expression/spel/ast/OpMinus.java

@@ -54,6 +54,17 @@ public OpMinus(int startPos, int endPos, SpelNodeImpl... operands) {
 	}
 
 
+	/**
+	 * Determine if this operator is a unary minus and its child is a
+	 * {@linkplain Literal#isNumberLiteral() number literal}.
+	 * @return {@code true} if it is a negative number literal
+	 * @since 6.1
+	 */
+	public boolean isNegativeNumberLiteral() {
+		return (this.children.length == 1 && this.children[0] instanceof Literal literal &&
+				literal.isNumberLiteral());
+	}
+
 	@Override
 	public TypedValue getValueInternal(ExpressionState state) throws EvaluationException {
 		SpelNodeImpl leftOp = getLeftOperand();
@@ -206,15 +217,4 @@ public void generateCode(MethodVisitor mv, CodeFlow cf) {
 		cf.pushDescriptor(this.exitTypeDescriptor);
 	}
 
-	/**
-	 * Check whether this operator is an unary minus and it's child is a number.
-	 * @return true if it is a negative number
-	 */
-	public boolean isNegativeNumber() {
-		if (children.length == 1 && children[0] instanceof Literal) {
-			return ((Literal) children[0]).isNumberLiteral();
-		}
-		return false;
-	}
-
 }