Run one testsuite with observers enabled in CI (#13869)

Signed-off-by: Bob Weinand <bobwei9@hotmail.com>

Include internal functions in the observer API

There are two main motivations to this:
a) The logic for handling internal and userland observation can be unified.
b) Unwinding of obs

Include internal functions in the observer API

There are two main motivations to this:
a) The logic for handling internal and userland observation can be unified.
b) Unwinding of observed functions on a bailout does notably not include observers. Even if users of observers were to ensure such handling themselves, it would be impossible to retain the relative ordering - either the user has to unwind all internal observed frames before the automatic unwinding (zend_observer_fcall_end_all) or afterwards, but not properly interleaved.

Signed-off-by: Bob Weinand <bobwei9@hotmail.com>

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Add an API to manipulate observers at runtime

Signed-off-by: Bob Weinand <bobwei9@hotmail.com>