Allow overriding SpeechOptions URL query parameters

`SpeechOptions.path` and `SpeechOptions.params` are internal. We should rename them to `abridgedPath` and `urlQueryItems`, respectively, and make them `open`, for consistency with `RouteOptions` in MapboxDirections. This will enable developers to pass in additional settings that aren’t supported by this library, such as beta parameters that it can’t support due to backwards compatibility concerns.

https://github.com/mapbox/mapbox-speech-swift/blob/b0a6008c184c1010dac11e14bf20afe4261d8c36/Sources/MapboxSpeech/MBSpeechOptions.swift#L65 https://github.com/mapbox/mapbox-speech-swift/blob/b0a6008c184c1010dac11e14bf20afe4261d8c36/Sources/MapboxSpeech/MBSpeechOptions.swift#L74

/ref mapbox/mapbox-directions-swift#343 mapbox/mapbox-directions-swift#461
/cc @mapbox/navigation-ios @browndp08 @Guardiola31337

Start in Sources/MapboxSpeech/MBSpeechOptions.swift at the linked SpeechOptions.path and SpeechOptions.params declarations, then compare the corresponding RouteOptions API in MapboxDirections. Rename the properties to abridgedPath and urlQueryItems and make them open so callers can provide additional query settings; verify the project still builds and existing behavior is preserved.

Written by the indexing model from the issue text.