Add a special notification unlink available only for modules (#9406)

Add a new module event `RedisModule_Event_Key`, this event is fired
when a key is removed from the keyspace.
The event includes an open key that can be used for reading the key before
it is removed. Modules can also extract the key-name, and use RM_Open
or RM_Call to access key from within that event, but shouldn't modify anything
from within this event.

The following sub events are available:
  - `REDISMODULE_SUBEVENT_KEY_DELETED`
  - `REDISMODULE_SUBEVENT_KEY_EXPIRED`
  - `REDISMODULE_SUBEVENT_KEY_EVICTED`
  - `REDISMODULE_SUBEVENT_KEY_OVERWRITE`

The data pointer can be casted to a RedisModuleKeyInfo structure
with the following fields:
```
     RedisModuleKey *key;    // Opened Key
 ```

### internals

* We also add two dict functions:
  `dictTwoPhaseUnlinkFind` finds an element from the table, also get the plink of the entry.
  The entry is returned if the element is found. The user should later call `dictTwoPhaseUnlinkFree`
  with it in order to unlink and release it. Otherwise if the key is not found, NULL is returned.
  These two functions should be used in pair. `dictTwoPhaseUnlinkFind` pauses rehash and
  `dictTwoPhaseUnlinkFree` resumes rehash.
* We change `dbOverwrite` to `dbReplaceValue` which just replaces the value of the key and
  doesn't fire any events. The "overwrite" part (which emits events) is just when called from `setKey`,
  the other places that called dbOverwrite were ones that just update the value in-place (INCR*, SPOP,
  and dbUnshareStringValue). This should not have any real impact since `moduleNotifyKeyUnlink` and
  `signalDeletedKeyAsReady` wouldn't have mattered in these cases anyway (i.e. module keys and
  stream keys didn't have direct calls to dbOverwrite)
* since we allow doing RM_OpenKey from withing these callbacks, we temporarily disable lazy expiry.
* We also temporarily disable lazy expiry when we are in unlink/unlink2 callback and keyspace 
  notification callback.
* Move special definitions to the top of redismodule.h
  This is needed to resolve compilation errors with RedisModuleKeyInfoV1
  that carries a RedisModuleKey member.

Co-authored-by: Oran Agra <oran@redislabs.com>

src/t_string.c

@@ -612,7 +612,7 @@ void incrDecrCommand(client *c, long long incr) {
     } else {
         new = createStringObjectFromLongLongForValue(value);
         if (o) {
-            dbOverwrite(c->db,c->argv[1],new);
+            dbReplaceValue(c->db,c->argv[1],new);
         } else {
             dbAdd(c->db,c->argv[1],new);
         }
@@ -667,7 +667,7 @@ void incrbyfloatCommand(client *c) {
     }
     new = createStringObjectFromLongDouble(value,1);
     if (o)
-        dbOverwrite(c->db,c->argv[1],new);
+        dbReplaceValue(c->db,c->argv[1],new);
     else
         dbAdd(c->db,c->argv[1],new);
     signalModifiedKey(c,c->db,c->argv[1]);