#132: Provide alternative audio source for text-to-speech

[aaronhktan]

Description

This PR adds the ability to switch the text-to-speech engine away from Qt Speech (libspeechd on Linux, Sin-Ji or other voices on macOS, etc.) to a series of audio files downloaded from Google TTS.

This alternative works as follows:

• User chooses Google TTS in the Advanced settings pane.
• User is prompted to do a one-time download of the audio files.
• After download is complete and files are unzipped, user clicks on the speaker button for Cantonese or Mandarin.
• The Jyutping or Pinyin for a phrase is split into a list of syllables using ChineseUtils::segmentJyutping or ChineseUtils::segmentPinyin respectively.
• The audio file for each syllable is played. (For example, hoi1 wui2 => Jyut Dictionary plays hoi1.mp3 and wui2.mp3.)

Closes #132.

Type of change

• [x] New feature (non-breaking change which adds functionality)

How Has This Been Tested?

Test Configuration:

• Tested default behaviour (downloading audio files successfully and switching to Google TTS).

• Tested interrupted download (disabling Wi-Fi/ethernet during download), making sure that error code was displayed.

• [x] macOS

• OS and version: macOS 14.1 Sonoma

• Toolchain: Xcode 15 clang/clang++

• Qt Version: 5.15.12, provided by KDE craft

• [x] Ubuntu

• OS and version: Pop!_OS 22.04

• Toolchain: g++ (Ubuntu 11.4.0-1ubuntu1~22.04) 11.4.0

• Qt Version: 5.15.2

• [x] Windows

• OS and version: Windows 11 22H2 22621.1555

• Toolchain: MinGW 8.1.0

• Qt Version: 5.15.12, provided by KDE craft

Checklist:

• [x] My code follows the style guidelines of this project (black for Python code, .clang-format in the src/jyut-dict directory for C++)
• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have translated my user-facing strings to all currently-supported languages
• [x] I have made corresponding changes to the documentation