Why this change?
Before this change, the error messages returned when validating theme
settings of typed objects was an array of array instead of just an
array.
Why this change?
```
some_setting:
default: 0
type: string
```
A theme setting like the above will cause an error to be thrown on the
server when importing the theme because the default would be parsed as
an integer which caused an error to be thrown when we are validating the
value of the setting.
What does this change do?
Convert the value to a string when working with string typed theme
settings.
Why this change?
This change adds validation for the default value for `type: objects` theme
settings when a setting theme field is uploaded. This helps the theme
author to ensure that the objects which they specifc in the default
value adhere to the schema which they have declared.
When an error is encountered in one of the objects, the error
message will look something like:
`"The property at JSON Pointer '/0/title' must be at least 5 characters
long."`
We use a JSON Pointer to reference the property in the object which is
something most json-schema validator uses as well.
What does this change do?
1. This commit once again changes the shape of hash returned by
`ThemeSettingsObjectValidator.validate`. Instead of using the
property name as the key previously, we have decided to avoid
multiple levels of nesting and instead use a JSON Pointer as the key
which helps to simplify the implementation.
2 Introduces `ThemeSettingsObjectValidator.validate_objects` which
returns an array of validation error messages for all the objects
passed to the method.
Why this change?
The logic for validating a theme setting's value and default value was
not consistent as each part of the code would implement its own logic.
This is not ideal as the default value may be validated differently than
when we are setting a new value. Therefore, this commit seeks to
refactor all the validation logic for a theme setting's value into a
single service class.
What does this change do?
Introduce the `ThemeSettingsValidator` service class which holds all the
necessary helper methods required to validate a theme setting's value
