Introduced placeholder support for Headers tag attributes

Added the functionality to allow the disabled and defaults-disabled
attribute of <header> tag to accept a placeholder and resolve it during
parsing.

- Updated the spring-security .rnc files starting from 4.2 up to 5.2
with xsd:token type instead of boolean
- Added unit tests for headers.disabled and headers.defaults-disabled
attributes with placeholder
- Modified the HeadersBeanDefinitionParser to support resolving
placeholders
- Updated spring.schemas to point to latest spring-security-5.2.xsd

Fixes gh-6547

config/src/test/resources/org/springframework/security/config/http/HttpHeadersConfigTests-DefaultsDisabledWithPlaceholder.xml

@@ -0,0 +1,36 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+  ~ Copyright 2002-2019 the original author or authors.
+  ~
+  ~ Licensed under the Apache License, Version 2.0 (the "License");
+  ~ you may not use this file except in compliance with the License.
+  ~ You may obtain a copy of the License at
+  ~
+  ~      http://www.apache.org/licenses/LICENSE-2.0
+  ~
+  ~ Unless required by applicable law or agreed to in writing, software
+  ~ distributed under the License is distributed on an "AS IS" BASIS,
+  ~ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+  ~ See the License for the specific language governing permissions and
+  ~ limitations under the License.
+  -->
+
+<b:beans xmlns:b="http://www.springframework.org/schema/beans"
+		xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+		xmlns="http://www.springframework.org/schema/security"
+		xsi:schemaLocation="
+			http://www.springframework.org/schema/security
+			http://www.springframework.org/schema/security/spring-security.xsd
+			http://www.springframework.org/schema/beans
+			http://www.springframework.org/schema/beans/spring-beans.xsd">
+
+	<http auto-config="true">
+		<headers defaults-disabled="${security.headers.defaults.disabled}"/>
+	</http>
+
+	<b:bean name="propertyPlaceholderConfigurer" class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer"/>
+
+	<b:bean name="simple" class="org.springframework.security.config.http.HttpHeadersConfigTests.SimpleController"/>
+
+	<b:import resource="userservice.xml"/>
+</b:beans>

config/src/test/resources/org/springframework/security/config/http/HttpHeadersConfigTests-DisabledWithPlaceholder.xml

@@ -0,0 +1,36 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+  ~ Copyright 2002-2019 the original author or authors.
+  ~
+  ~ Licensed under the Apache License, Version 2.0 (the "License");
+  ~ you may not use this file except in compliance with the License.
+  ~ You may obtain a copy of the License at
+  ~
+  ~      http://www.apache.org/licenses/LICENSE-2.0
+  ~
+  ~ Unless required by applicable law or agreed to in writing, software
+  ~ distributed under the License is distributed on an "AS IS" BASIS,
+  ~ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+  ~ See the License for the specific language governing permissions and
+  ~ limitations under the License.
+  -->
+
+<b:beans xmlns:b="http://www.springframework.org/schema/beans"
+		xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+		xmlns="http://www.springframework.org/schema/security"
+		xsi:schemaLocation="
+			http://www.springframework.org/schema/security
+			http://www.springframework.org/schema/security/spring-security.xsd
+			http://www.springframework.org/schema/beans
+			http://www.springframework.org/schema/beans/spring-beans.xsd">
+
+	<http auto-config="true">
+		<headers disabled="${security.headers.disabled}" />
+	</http>
+
+	<b:bean name="propertyPlaceholderConfigurer" class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer"/>
+
+	<b:bean name="simple" class="org.springframework.security.config.http.HttpHeadersConfigTests.SimpleController"/>
+
+	<b:import resource="userservice.xml"/>
+</b:beans>