PostGIS improvements

PostGIS extension for PGlite

As of PGlite v0.4.0, PostGIS extension is supported as experimental.

This issue tracks the known limitations and further needed improvements.

Limitations

• no Gdal support (added in 0.5.1)
• no C++ exception handling (any thrown exception will hang or terminate the PGlite instance)
• no protobuf-c support

Bundling

The bundling of the (external) extension PostGIS needs improvement, in particular the way its external dependencies (libs) are delivered. Right now they are statically linked as whole archives (including libstdc++!) which is not ideal. A better way would be to build them as dynamic libs and package them in the same deliverable.

In particular, one of the issues is that the extension itself consists of two libraries and the order in which they are loaded matters! There is some hacking in extensionUtils that fixes this for the moment, but a better way would be to handle this properly in the extension's setup/init functions.