4GB memory support

The support for 4GB memory space is available by adding the following configuration:

<ItemGroup>
    <WasmShellExtraEmccFlags Include="-s MAXIMUM_MEMORY=4GB"/>
</ItemGroup>

The configuration can also be detected at runtime using the UNO_BOOTSTRAP_EMSCRIPTEN_MAXIMUM_MEMORY environment variable, which will be set to 4GB once set.