Support HTML markup for knob labels

[liushuyu]

Add HTML rich text support for knob label

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This change is 

[jasp00]

This is another example of why #3071 should be solved. Most of this patch is about format changes.

Regarding the main purpose, what kind of HTML effects do you plan to use that cannot be done through the style sheet? Is this feature for knob labels only or will this be extended to all labels?

[liushuyu]

This is another example of why #3071 should be solved. Most of this patch is about format changes.

Right... That's because I have integrated a code formatter in git commit hook. So each time I commit something, the changed files will be formatted.

Regarding the main purpose, what kind of HTML effects do you plan to use that cannot be done through the style sheet? Is this feature for knob labels only or will this be extended to all labels?

Well, that's relating to some chatter in our chat room: multi-line labels are not supported in knob labels, either <br> tag or \n didn't work at all.

[jasp00]

multi-line labels are not supported in knob labels

Have you tried using QLabel?

[liushuyu]

Have you tried using QLabel?

QLabel works though.

[tresf]

@liushuyu what is our decision on this? We can support HTML labels if it helps things, but I have to agree with @jasp00 about the unnecessary code formatting.

[husamalhomsi]

Bumping. ^

[PhysSong]

I reverted some formatting changes and resolved conflicts. There are some things to change more, e.g., fix a memory from m_tdRenderer by either setting QObject ownership or using std::unique_ptr, replacing <font> with style attribute.

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Linux

• Linux (AppImage): lmms-1.3.0-alpha.1.72%2Bgfe48bfb-linux-x86_64.AppImage (build link)

Windows

• Windows 32-bit: lmms-1.3.0-alpha.1.72%2Bgfe48bfbef-mingw-win32.exe (build link)
• Windows 64-bit: lmms-1.3.0-alpha.1.72%2Bgfe48bfbef-mingw-win64.exe (build link)
• Windows 32-bit: lmms-1.3.0-alpha-msvc2017-win32.exe (build link)
• Windows 64-bit: lmms-1.3.0-alpha-msvc2017-win64.exe (build link)

macOS

• macOS : lmms-1.3.0-alpha.1.72%2Bgfe48bfbef-mac10.14.dmg (build link)

🤖

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[PhysSong]

It's now ready to review/merge.