fix(RasterTile): partial loading for raster tiles

[airnez]

Description

Sets a new way to request data from DataSource provider : partial loading. If it is enabled, the command execution is considered successful as soon as one of the data loading promise is successful. It returns the same results array than before but includes null for failed requests. The caller takes responsibility for handling those null values.

Motivation and Context

See issue 2311. It more broadly fixes glitches whitnessed when rendering reprojected raster (or ratserized) data sources . It especially occurres from far away or on data source boundaries, when projecting (epsg:3857) data on the globe (epsg:4326). This seems to correspond to issue 2395

Screenshots

See before / after comparison for this layer :

            var wmtsSource = new itowns.WMTSSource({
                url: 'https://data.geopf.fr/wmts?SERVICE=WMTS&VERSION=1.0.0&REQUEST=GetCapabilities',
                crs: 'EPSG:3857',
                name: 'GEOGRAPHICALGRIDSYSTEMS.EDUGEO.LYON1947',
                tileMatrixSet: 'PM_6_16',
                version: '1.0.0',
                style: 'normal',
                format: 'image/png',
            });

Before fix

partial-loading-bug.mp4

After fix

partial-loading-fix.mp4