[ExportSystemC] Support more emitc operations and types

[maerhart]

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• Implement emission patterns for all emitc operations except variable for which we have our own implementation. Support for template arguments to function calls is not added yet, but can be easily added when there is a need.
• Add emission pattern support for attributes: this is helpful for operations like emitc.constant which can take any attribute and print it. Having them pattern based allows for more modularity and reuse.
• Move the helper function to emit parentheses around an expression to the InlineEmitter to share it across the various files implementing emission patterns and allow for easier use.