Include libspeechd for SpeechSynthesis support

[hypevhs]

Electron apps may want to use the SpeechSynthesis part of the Web Speech API.

On Linux, this is gated behind the --enable-speech-dispatcher flag. If enabled, Chromium will attempt to dynamically load the Speech Dispatcher library libspeechd.so.2. If not present, speech is disabled. Chromium source code for proof. Right now this library isn't included inside the Flatpak, even though the host may be fully configured with Speech Dispatcher.

This PR builds and includes the library (but not the daemon) so that TTS stuff can easily work as long as the consuming app passes the --enable-speech-dispatcher flag and has sandbox perms for --filesystem=xdg-run/speech-dispatcher.

This is useful for flathub/dev.vencord.Vesktop#20, though we thought it'd make sense to upstream it for other apps' benefit.

[flathubbot]

Started test build 131050

[flathubbot]

Build 131050 successful To test this build, install it from the testing repository:

flatpak install --user https://dl.flathub.org/build-repo/114049/org.electronjs.Electron2.BaseApp.flatpakref

[flathubbot]

Started test build 131055

[flathubbot]

Build 131055 failed

[bbhtt]

bot, build

[flathubbot]

Queued test build for org.electronjs.Electron2.BaseApp.

[flathubbot]

Started test build 131058

[flathubbot]

Build 131058 successful To test this build, install it from the testing repository:

flatpak install --user https://dl.flathub.org/build-repo/114057/org.electronjs.Electron2.BaseApp.flatpakref

[bbhtt]

Thanks.