Lyrics: load sidecar .lrc file as song lyrics

Reason for the change

It's common to see lyrics file (.lrc file) as a sidecar file. Currently Elisa only attempts to load lyrics lived in the ID3 tag and ignores the sidecar .lrc file, this MR attempts to address this pain point.

See also:

• https://discuss.kde.org/t/about-elisas-support-for-local-lyric-files/14481/4
• https://bugs.kde.org/show_bug.cgi?id=465716
• !464 (closed) (while my implementation is much simplified compared to !464 (closed))

Test plan

I only tested it manually on my machine. Test steps are:

1. Prepare: Assume there is a regular audio file called sample_track.mp3, you need to prepare a sample_track.lrc file with valid lyrics content.
2. Use Elisa to play sample_track.mp3.
3. See result.

Screenshots or screen recordings

While I also use Elisa on Linux desktop, I did the fix under Windows with MSYS2 so the screenshot is taken under Windows. The dark theme is broken so I took the screenshot under light theme (the previously mentioned icon issue was also fixed by me in !632 (merged), screenshot updated accordingly).

Before	After
I guess we don't need a "before" image here...

Bugs fixed

BUG: https://bugs.kde.org/show_bug.cgi?id=465716

cc @aacid