Make the indent size configurable for an JsonText instance

[daxian-dbw]

Today, the indent size for rendering a JsonText instance is hard coded to be 3 spaces. For a deep JSON object, it'd nice if I can set the indent size to be 2 to have more rendered within the same console space. So, I propose to make the indent size configurable for an JsonText instance.

The change should be simple:

1. Update JsonBuilderContext
   • Add a read-only property int IndentWidth
   • Update the constructor take another parameter int indentWidth, and assign its value to the read-only property IndentWidth
   • Update the InsertIndentation method to have Indentation * IndentWidth instead.
2. Add a new read-write property IndentWidth to JsonText to allow user set value
   • Use 3 as the default value so the default behavior is unchanged.
   • Pass it in when creating the JsonBuilderContext instance in the Build() method.

I think it may be reasonable to make sure the value assigned to IndentWidth is between 2 and 4 inclusively, to make user only choose from 2, 3, or 4 spaces.

If maintainers are willing to accept this change, I'm happy to submit a PR for it.