The extension state is not easily accessible in release builds, which
makes debugging issue with the loader very difficult. This commit
introduces a new schema `_timescaledb_debug` and makes the function
`ts_extension_get_state` available also in release builds as
`_timescaledb_debug.extension_state`.
See #1682
This will move the definitions of `debug_waitpoint_enable`,
`debug_waitpoint_disable`, and `debug_waitpoint_id` to always be
defined for debug builds and modify existing tests accordingly.
This means that it is no longer necessary to generate isolation test
files from templates (in most cases), and it will be straightforward to
use these functions in debug builds.
The debug utilities can be disabled by setting the option
`ENABLE_DEBUG_UTILS` to `OFF`.
