…ints

Dynamically defined endpoints can now have their own block of storage
(to be provided by the caller of emberAfSetDynamicEndpoint()).

If no storage is set for a dynamic endpoint, it behaves exactly as before,
which is treating all attributes as "external", regardless of the respective
bit in the attribute's metadata.

With a storage provided, attributes behave the same way as static endpoint's
do, that is, only those marked "external" need to be handled programmatically
in the respective callbacks, other attributes' storage is automatic.

Instead of re-creating dynamic endpoint's cluster declarations
using the DECLARE_DYNAMIC_xxx macros, the new
`setupDynamicEndpointDeclaration()` function allows setting
up a dynamic endpoint by using clusters defined in another
endpoint as templates. Usually that is a disabled endpoint created
in ZAP with all possibly dynamically used clusters assigned.

In combination with dynamic endpoint attribute storage, this
greatly simplifies implementing dynamic endpoints and allows
configuring them using the ZAP tool to ensure specs conformance,
much the same way as with statically defined endpoints.

...to allow differentiating server and client sides of the same cluster type

to allow checking that it has sufficient size

more readable attributeLocation calculation, remove unneeded ugly C cast

- af-types needs platform/CHIPDeviceConfig.h for CHIP_DEVICE_CONFIG_DYNAMIC_ENDPOINT_COUNT
- reflect this in BUILD.gn by adding the platform_config_header sourceset as dependency
- remove unneeded comment lines in agreement with original author

- check passed in endpointType is explicitly "empty" (zeroed out)
- use CanCastTo instead of literally testing against 255
- return appropriate errors
- only return completely set-up or untouched endpointType
- no const cast needed

… code

Turns out that while this works well on current compilers, it does not with many embedded toolchains.

- idea was that an if testing an always false constexpr bool should
  skip *compiling* its body.

- we need that because that body refers to a struct field that is non-existing
  in the case when the if condition is constexpr false

- note that we can't use a real >=C++17 constexpr if, because in the
  CHIP_DEVICE_CONFIG_DYNAMIC_ENDPOINT_COUNT>0 case, the condition cannot be a constexpr

Bottom line: there seems no way around the uglier #ifdef around the `else if` clause.
We can avoid an #ifdef in the middle of a condition expression.

… int size result on some platforms

- took the chance to add safe error exit on excessive cumulative cluster storage size.
- using `typeof()` and `CanCastTo` throughout to make code independent of struct field sizes.

Co-authored-by: Andrei Litvin <[email protected]>