Browse element folding nested lists and <img> icons

[AntonKhorev]

#5317 with additions:

• tagless way nodes with equal other ways are grouped together (otherwise it's the main expected source of vertical space waste)
• icons written as 20x20 elements + line heights inside lists also set to 20px = hopefully acceptable icon alignment, see Improve scaling and vertical alignment of browse icons #5354 (comment); sometimes 1.25rem is used instead of 20px for better scaling and alignment with text-only zooming, see Set layer button size relative to font size #5067

Icon initializer like in #5080, but .yml is different.

Old vs new alignment:
vs

Text-only zoom

50%:

150%:

[github-actions]

	1 Warning
⚠️	Number of updated lines of code is too large to be in one PR. Perhaps it should be separated into two or more?

Generated by 🚫 Danger