Changes

Use status 400 for field validation errors (DAD-379) #497 (#502)

* Use status 400 for field validation errors (DAD-379) #497

* Mandatory and not updateable column validation for update

* Move mandatory fields validation from DefaultPOSerializer to before save event handler.

* Fix potential event handler leak

- incorporate other coderabbitai suggestions

* Fix event handler registration

- add SALESREP_ID and AD_USER_NAME to context to make it more consistent
with Web Client
- fix setDefaultValue not ignoring key and uuid
column/home/hengsin/workspace/pcn/idempiere-rest/com.trekglobal.idempiere.rest.api/src/com/trekglobal/idempiere/rest/api/v1/resource/impl/ModelResourceImpl.java

* Handle explicit JsonNull and isJsonPrimitive

* Translate validForeignKeysEx and CrossTenantException to bad request exception

* Move setDefaultValue and validate mandatory fields to before save event handler.

* Fix potential NPE

* Incorporate patch from Carlos to fix update of context and default parsing

* Simplify loop detection

* Don't fill default value for update

- Surface IDempiereRestException for createChild.

* Add null check for dependentColumn
 (commit: 30806f1)