[feature request] Allow for complex Item metadata in .item files

[5iver]

Currently, Item metadata in .item files is limited to strings, numbers and booleans. Metadata objects are able to contain collections, which allows a hierarchical structure of the keys in the metadata. For example, this Item definition...

Switch      Test_Switch_1           "Test Switch 1 [%s]"            <switch>      (gVirtual,gTest)                      { Test_Namespace="Test_Value" [Test_Key_1={Test_Subkey_1="Test_value_1", Test_Subkey_2=false, Test_Subkey_3=5}] }

... causes the following to be logged...

2020-05-27 15:46:28.136 [WARN ] [org.eclipse.smarthome.model.core.internal.ModelRepositoryImpl] - Configuration model 'test.items' has errors, therefore ignoring it: [16,163]: no viable alternative at input '{'
[16,230]: extraneous input '}' expecting ']'

Using the Jython or Javascript helper libraries, Item metadata can be set with a hierarchical key structure, which is not possible in an .items file...

from core.metadata import set_metadata, get_metadata, get_key_value

from core.log import logging, LOG_PREFIX#, log_traceback
LOG = logging.getLogger("{}.TEST_2".format(LOG_PREFIX))

set_metadata("Test_Switch_1", "Test_Namespace", {"Test_Key_1": {"Test_Subkey_1": "Test_value_1", "Test_Subkey_2":False, "Test_Subkey_3":5}}, "Test_Value")

LOG.warn("Test_Switch_1: {}".format(get_metadata("Test_Switch_1", "Test_Namespace")))
LOG.warn("Test_Key_1: {}".format(get_key_value("Test_Switch_1", "Test_Namespace", "Test_Key_1")))
LOG.warn("Test_Subkey_1: {}".format(get_key_value("Test_Switch_1", "Test_Namespace", "Test_Key_1", "Test_Subkey_1")))
LOG.warn("Test_Subkey_2: {}".format(get_key_value("Test_Switch_1", "Test_Namespace", "Test_Key_1", "Test_Subkey_2")))
LOG.warn("Test_Subkey_3: {}".format(get_key_value("Test_Switch_1", "Test_Namespace", "Test_Key_1", "Test_Subkey_3")))

2020-05-27 15:52:48.992 [WARN ] [jython.TEST_2] - Java version [Java-1.8.0_242-OpenJDK_64-Bit_Server_VM,_25.242-b08,_Oracle_Corporation-on-Linux-5.4.10-200.fc31.x86_64-amd64]
2020-05-27 15:52:48.994 [WARN ] [jython.TEST_2] - Test_Switch_1: Metadata [key=Test_Namespace:Test_Switch_1, value=Test_Value, configuration=[Test_Key_1={'Test_Subkey_3': 5, 'Test_Subkey_1': 'Test_value_1', 'Test_Subkey_2': False}]]
2020-05-27 15:52:48.994 [WARN ] [jython.TEST_2] - Test_Key_1: {'Test_Subkey_3': 5, 'Test_Subkey_1': 'Test_value_1', 'Test_Subkey_2': False}
2020-05-27 15:52:48.995 [WARN ] [jython.TEST_2] - Test_Subkey_1: Test_value_1
2020-05-27 15:52:48.995 [WARN ] [jython.TEST_2] - Test_Subkey_2: 0
2020-05-27 15:52:48.996 [WARN ] [jython.TEST_2] - Test_Subkey_3: 5

Using Jython and the core.metadata module, you can create structures like this, which is not currently possible with a text-based Items file...

"Mode": {
    "Morning": {"low_lux_trigger":5, "Level":10},
    "Day":{"low_lux_trigger":50, "Level":45},
    "Evening":{"low_lux_trigger":50, "Level":45},
    "Night":{"low_lux_trigger":50, "Level":30},
    "Late":{"low_lux_trigger":5, "Level":1}
}
"Timer": {
    "Action": {
        "ON": {
            "Time":60,
            "Recurring":False
        },
        "OFF": {
            "Time":3600,
            "Recurring":False
        }
    },
    "Notification": {
        "ON": {
            "Time":3600,
            "Message": "The doors are currently unlocked",
            "Types": {
                "Audio": True,
                "Kodi": True,
                "Mobile": True
            },
            "Priority": 0,
            "Recurring":True
        },
        "OFF": {
            "Time":5,
            "Recurring":False
        }
    }
}

https://github.com/openhab/openhab-core/blob/master/bundles/org.openhab.core.model.item/src/org/eclipse/smarthome/model/item/internal/GenericItemProvider.java#L341