Increase default STACK_SIZE when compiling highs

Build is currently using emscripten default STACK_SIZE when compiling highs, [which is 64KB](https://emscripten.org/docs/tools_reference/settings_reference.html#stack-size), and may be insufficient for many models. This MR increases the STACK_SIZE when compiling to 4MB and adds a test that fails when using a 64KB stack.