feat(formatting/#785): Default format provider when no extension provider

[bryphe]

This completes the formatting work for #785 to hook up the = expression to format.

Currently, we rely on a range formatter and/or a document formatter to be available in order to process formats. This adds a basic default strategy, using the language configuration (increaseIndentExpression / decreaseIndentExpression) to apply formatting edits, if there is no extension available.

Fixes #785

Todo:

• Get correct language configuration for buffer
• Hook up format logic
• Hook up range evaluations