Clarify a little bit the usage of stdClass() and (object)[]

Following a discussion @ Moodle Dev Chat:

https://moodle.org/local/chatlogs/index.php?conversationid=23025

This is about to try to improve/clarify a little bit the use of both new stdClass() and (object) [] constructors to get an "object" (stdClass) instance. And apply it to (the end of):

https://docs.moodle.org/dev/Coding_style#Classes

This is the proposal to start the discussion about:

a) By default, new stdClass() should be used, and not the empty casting (object) [] alternative. Note a backslash may be needed under namespaced stuff. And using use stdClass; is highly discouraged.

b) phpdocs should also use stdClass and not object or any other alternative. This is already @ https://docs.moodle.org/dev/Coding_style#Types.

c) When objects are being created with properties, it's allowed to use $obj = (object) ['data' => 'value'];. Of course it's perfectly valid to use $obj = new stdClass(); $obj->data = 'value';.

d) When objects are being created without properties, but in a context of other objects being created with properties as specified in c) (say a data provider or a big structure... ) then it's allowed to use the empty casting (object) []. Exclusively for readability in a context.

e) Any other use of empty casting apart from the exception in d) is not allowed.