web: Use wasm exception when enabled

[Faless]

Depends on godotengine/godot#124118 which compiles the main runtime with exceptions enabled.

[dsnopek]

What happens if someone builds with this flag and their extension is loaded in an older version of Godot that doesn't have godotengine/godot#124118?

Since we now support building extensions for Godot 4.3+ from a single version of godot-cpp, do we need to add a version check for using this flag?

Something like:

def parse_version(v):
    return tuple(int(x) for x in v.split("."))

def generate(env):
    # ...
    if not env["disable_exceptions"] and parse_version(env["api_version"]) >= (4, 8):
        env.Append(CCFLAGS=["-fwasm-exceptions"])
        env.Append(LINKFLAGS=["-fwasm-exceptions"])