LibWeb: Introduce Content Security Policy policies and directives

These form the basis of Content Security Policy. A policy is a
collection of directives that are parsed from either the
Content-Security-Policy(-Report-Only) HTTP header, or the `<meta>`
element.

The directives are what restrict the operations can be performed in the
current global execution context. For example, "frame-ancestors: none"
tells us to prevent the page from being loaded in an embedded context,
such as `<iframe>`.

You can see it a bit like OpenBSD's pledge() functionality, but for the
web platform: https://man.openbsd.org/pledge.2

Libraries/LibWeb/CMakeLists.txt

@@ -36,6 +36,13 @@ set(SOURCES
     Clipboard/ClipboardItem.cpp
     Compression/CompressionStream.cpp
     Compression/DecompressionStream.cpp
+    ContentSecurityPolicy/Directives/Directive.cpp
+    ContentSecurityPolicy/Directives/DirectiveFactory.cpp
+    ContentSecurityPolicy/Directives/Names.cpp
+    ContentSecurityPolicy/Directives/SerializedDirective.cpp
+    ContentSecurityPolicy/Policy.cpp
+    ContentSecurityPolicy/PolicyList.cpp
+    ContentSecurityPolicy/SerializedPolicy.cpp
     CredentialManagement/Credential.cpp
     CredentialManagement/CredentialsContainer.cpp
     CredentialManagement/FederatedCredential.cpp