fix: improve comments in IPluginExecutor interface

[jaypaik]

#36 erroneously added strict restrictions on what a plugin can call.

Currently in v0.6.0:

interface IPluginExecutor {
    /// @notice Method from calls made from plugins.
    /// @param data The call data for the call.
    /// @return The return data from the call.
    function executeFromPlugin(bytes calldata data) external payable returns (bytes memory);

    /// @notice Method from cals made from plugins.
    /// @dev If the target is a plugin, the call SHOULD revert.
    /// @param target The target of the external contract to be called.
    /// @param value The value to pass.
    /// @param data The data to pass.
    function executeFromPluginExternal(address target, uint256 value, bytes calldata data) external payable;
}

[huaweigu]

If executeFromPluginExternal is responsible for non-plugin address, can this method call into non-plugin address (e.g. wallet native functions)?

[jaypaik]

Yes, we don't explicitly prohibit this in the standard (hence the correction made here from the erroneous change from prior PRs: #32, #36). The reference implementation has chosen to disallow calls to native functions, but it can be done. Perhaps worthwhile to define in the standard in a future update though, since it impacts how plugins are written.