[5.1] Core loader custom element rework

[C-Lodder]

Summary of Changes

This PR has three parts:

1. The core loader custom element has been rewritten to use an SVG rather than built using CSS.
2. We can now pass inline="true" and size="xx", allowing us to have an inline instance, rather than fullscreen.
3. The sample data module now uses the updated core loader, rather than an old animated GIF.

Why SVG over CSS?
The original CSS version has loads of hardcoded values, meaning scaling became extremely difficult.

Why aren't we observing the inline or size attributes?
Simply because I do not believe they need observing.

Testing Instructions

1. Run npm i
2. Go to your Joomla backend
3. Install the sample data

Screenshot

Thank you to @dgrammatiko for providing the SVG.

[Quy]

Would you consider this to be a fix for #31078 #30099?

[dgrammatiko]

Nice one Charlie. Quick question: in the screenshots it seems that the logo is twisted (order of the colours). Was it my fault with the svg?

[C-Lodder]

@dgrammatiko Good catch, fixed.

@Quy Probably not.

[Quy]

I have tested this item ✅ successfully on ef94d64

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[fgsw]

I have tested this item ✅ successfully on ef94d64

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[Quy]

RTC

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[LadySolveig]

Thank you @C-Lodder and for review and testing @dgrammatiko @fgsw @Quy