This commit fixes a number of bugs in `file_size_restriction` settings and does a little of refactoring to reduce duplicated code in site setting types (the refactoring is necessary to fix one of the bugs).
The bugs in `file_size_restriction` settings that are fixed in this commit:
1. Save/cancel buttons next to a `file_size_restriction` setting are shown upon navigating to the settings page without changes being made to the setting
2. Cancel button that discards changes made to the setting doesn't work
3. Reset button that resets the setting to its default doesn't work
4. Validation error message isn't cleared when resetting/cancelling changes
To repro those bugs, navigate to `/admin/site_settings/category/files` and observe the top 2 settings in the page (`max image size kb` and `max attachment size kb`).
Internal topic: t/134726.
Followup db993cf8fd
Since in the above commit we converted integer site settings
to actual integers then set that as the new `buffered.value`,
the overridden indicator technically thinks the value has changed,
even if the user sets it back to the default:
```
overridden: propertyNotEqual("setting.default", "buffered.value"),
```
We can fix this by converting the parsed integer back to a string
before setting the buffered setting value.
Followup to e113eff663
We previously sanitized input for integer site settings
on the server side only, which was a bit confusing when
users would enter e.g. 100.5 and end up with 1005, and
not see this reflected in the UI.
Now that we are using native number inputs for these settings,
we can improve the experience a bit by not allowing `.` or `,`
in the input, because it should be whole numbers only, and
add a step size of 1. All other characters are already prevented
in this native number input.
