MgLayerBase should be able to get the filter of layer definition

[christinebao]

This requirement is from ticket ​http://trac.osgeo.org/fusion/ticket/327: Query: The matched objects excluded by layer filter are listed in Query result.

Layer definition may have filter, for example:

<LayerDefinition xsi:noNamespaceSchemaLocation="LayerDefinition-1.3.0.xsd" version="1.3.0">
      <VectorLayerDefinition>
           <ResourceId>Library://Theme/Data/bayarea_cities.FeatureSource</ResourceId>
           <FeatureName>SHP_Schema:bayarea_cities</FeatureName>
           <FeatureNameType>FeatureClass</FeatureNameType>
           <Filter>Autogenerated_SDF_ID < 3</Filter>
           <Geometry>SHPGEOM</Geometry>

MgLayerBase has APIs for read resource Id, feature name and geometry, but there is no way to get filter. It's better to make MgLayerBase have an API GetFilter(), and return the filter inside layer definition.

[christinebao]

Add an new API in MgLayerBase:

    //////////////////////////////////////////////////////////////////
    /// \brief
    /// Gets the filter associated with this layer
    ///
    /// <!-- Syntax in .Net, Java, and PHP -->
    /// \htmlinclude DotNetSyntaxTop.html
    /// string GetFilter();
    /// \htmlinclude SyntaxBottom.html
    /// \htmlinclude JavaSyntaxTop.html
    /// String GetFilter();
    /// \htmlinclude SyntaxBottom.html
    /// \htmlinclude PHPSyntaxTop.html
    /// string GetFilter();
    /// \htmlinclude SyntaxBottom.html
    ///
    /// \return
    /// Returns the filter or an empty string if this layer is not a feature layer or doesn't have filter.
    ///
    virtual STRING GetFilter();  /// __get

The m_filter is assigned when parsing layer definition model, which is the same as feature source id, feature class name and geometry name.

[christinebao]

Attach patch ​https://trac.osgeo.org/mapguide/attachment/ticket/1154/GetFilterAPI.patch.

This is reviewed by Chris in ticket ​http://trac.osgeo.org/fusion/ticket/327.

[christinebao]

Submit the patch for fixing this defect.