If an override comes back as a variable containing a deep variable (e.g. `''${self:custom.${deep:1}, "fallback"}''`) or really any variable at all, it needs to be made a deep variable and paused for next iteration. Do this generally rather than only in the case of deep variables. See the test case for a circumstance that the prior fix didn't resolve. This more generalized handling improves the fix and solves a remaining issue we found locally.
Use the variable string from which the overwrite parameters were extracted as the replacement target (in the case of deep variable discovery) rather than the context property which represents the entire original value that the replacement is being waited upon. That context property can contain far more content than the overwrite string itself.
This avoids taking a deep value as a valid term within an overwrite
(defaulting) variable statement that will later resolve to undefined
but, as a deep variable string, is valid in immediate evaluation.
Fixes#5027
Add explanatory text:
```
This can result from latent connections but may represent a cyclic
variable dependency
```
Also, rather than messages such as:
```
Serverless Information ----------------------------------
##########################################################################################
Serverless Information ----------------------------------
# 0: 0 of 2 promises have settled
Serverless Information ----------------------------------
# 0: 2 unsettled promises:
Serverless Information ----------------------------------
# 0: foo waited on by: ${foo:}
Serverless Information ----------------------------------
# 0: foo waited on by: ${foo:}
Serverless Information ----------------------------------
##########################################################################################
```
Collate the message to read like:
```
Serverless Information ----------------------------------
##########################################################################################
# 0: 0 of 2 promises have settled
# 0: 2 unsettled promises:
# 0: foo waited on by: ${foo:}
# 0: foo waited on by: ${foo:}
# This can result from latent connections but may represent a cyclic
variable dependency
##########################################################################################
```
