Provides a content formatter add-on for an `ITextViewer`. A content formatter changes the formatting of a document region while preserving and correctly updating the positions of the document.

## Package Specification

`IContentFormatter` defines the concept of a text formatter. It collaborates with content type specific formatting stratgies (`IFormattingStrategy`) which for a given document region format the subregion with the matching content type. The package contains a default implementation of `IContentFormatter` (`ContentFormatter`).
Additionally, an implementation of `IContentFormatterExtension` is provided for text edit based formatting strategies. This implementation only accepts formatting strategies implementing the extension interface `IFormattingStrategyExtension`. These formatting strategies are required to handle the position updating of the document. To facilitate the work with these text edit based formatting strategies, a default implementation called `ContextBasedFormattingStrategy` is provided. Formatting strategies inheriting from this class are text edit based and behave context dependent. Depending on the formatting context that is passed to the content formatter, different preferences and modes can be used to format different parts of a document.

To set up a proper working text edit based content formatter, the following steps are needed:

- Create an instance of `IFormattingContext`. The default implementation `FormattingContext` already provides support for the conversion of preferences from a preference store to a map and vice versa. The method `getPreferenceKeys` usually has to be overridden to return the appropriate keys of the preferences used during the formatting process. Then register a map of preferences with the formatting context by calling `setProperty(String, Object)` with the property identifier `FormattingContextProperties.CONTEXT_PREFERENCES`.
- Create an instance of the text edit based content formatter class `MultiPassContentFormatter`. The document partitioning and its associated default content type have to be passed to the constructor. This information is needed since the content formatter is able to format documents according to arbitrary partitionings and default content types.
- Register the formatting strategies for the content types that have to be formatted. If a formatting strategy is registered as master strategy, it is automatically associated with the default content type of the specified partitioning. If the formatting strategy is registered as slave strategy, it is associated with the indicated content type during the registration. Note that the master strategy can also be registered as a slave strategy for a content type other than the default content type.
- Specify the proper formatting mode (see FormattingContextProperties):
  - For whole document formatting set the property `CONTEXT_DOCUMENT` of the created formatting context to `true`. This is equivalent to setting `CONTEXT_REGION` with a region spanning the whole document.
  - For multiple region formatting set the property `CONTEXT_REGION` of the formatting context. Note that the content formatter automatically aligns the offset of a region to a line start for the master formatting strategy, it also completes eventual partitions covered only partially by the region for the slave formatting strategies.
  - For explicit formatting of a partition with the formatting strategy registered for a certain content type use the property `CONTEXT_PARTITION`. Note that the region denoted by this property must correspond to a partition relative to the specified partitioning in the document to be formatted. The content type of this property overrides the content type of the partition in the document.
- Call the method `MultiPassContentFormatter#format(IDocument, IFormattingContext)` with the created formatting context and the document to be formatted.