strategy.convert_to_symbol() demo

A strategy demonstrating the new strategy.convert_to_symbol() and strategy.convert_to_account() functions introduced in Pine v5.

Try selecting a custom "Base Currency" under Properties to see how the conversion works.

Note: The conversion functions seem to work as expected on BTCUSD, but not on BTCUSDT. This is likely because USDT is not recognized as a currency.