Make it possible to override the zeroAt value

[arai-a]

Production | Deploy preview

Fixed #5730

This adds "Align the timeline start with the marker start" menu item to markers, which overrides the "zeroAt" value.

When overridden the menu buttons at the top of the page gets "Starting point moved to (timestamp)" button.
Clicking it resets the override.

Also this supports negative timestamp.
The timeline looks line the following when overridden.

[flodolo]

I don't think this concept is going to be clear to localizers. Is "zero" just the start?

[arai-a]

Good point. It comes from "getZeroAt" name, but it's not obvious.

Other options I can think of are the following:

• Override the start of the timeline with marker's start
• Set the start of the timeline with marker's start
• Override the timeline origin with marker's start
• Set the timeline origin with marker's start
• Start the timeline from marker's start

And the following for the menu button:

• Starts at 100ms
• Starts from 100ms
• Origin at 100ms
• Origin overridden to 100ms

Can I have your opinion?
If there are better labels, let me know.

[flodolo]

Let's wait for @canova and folks who understand the project — and target audience — better than me.

Personally, I would go with something like:

• Align the timeline start with the marker start(or Set… to).
• Starting point moved to 100ms

[arai-a]

Updated the label, added dedicate icon, and rebased

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.69%. Comparing base (0dd124f) to head (1ca1a1c).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5733      +/-   ##
==========================================
+ Coverage   85.67%   85.69%   +0.01%     
==========================================
  Files         315      315              
  Lines       31110    31141      +31     
  Branches     8472     8566      +94     
==========================================
+ Hits        26654    26685      +31     
  Misses       4026     4026              
  Partials      430      430              

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