Convert more markers to SVG

[hlfan]

Description

• Makes all¹ markers SVGs with a similar structure. (addresses retina compatible icons #850 (comment))
• Changes the note markers' ✔️, ❌ & ➕ to be drawn with a reused stroke instead of areas to reduce file size and to enable an easier switch to SVG marker elements for more dynamic pins in the future.
• Continues to use marker-shadow.png from leaflet

Footnotes

1. not the yellow marker as I don't have the colours for that one ↩

[AntonKhorev]

Is it more clear from the routing icons, which one is start/finish? Maybe the start icon doesn't need to be changed?

[AntonKhorev]

By the way https://antonkhorev.github.io/msvgen/

I'm trying to parametrize the markers by currentColor for situations where several markers are to be displayed at the same time, like search results. Still haven't done gradients.

[hlfan]

If you mean you need to create the gradients' stops from currentColor to use these like for the directions icons (meaning without JS) that would need color-mix or the relative color functions which have only been available in css for less than a year.
But given that parametrication building these from templates with Ruby could be a big later addition.

[hlfan]

Still haven't done gradients.

I've also fiddled around a bit, trying to make a marker-based solution here.
Still trying to get rid of the mask as a gradient workaround.

[hlfan]

I've decided to reduce this PR to just the conversion of the SVG pins. While modularizing and parametrizing the markers is a commendable effort, it shouldn't be part of this PR, but the next step instead.
I've removed from this PR:

• the marker renaming
• the two new direction markers
• the resizing to 25x40
• the new marker outline paths since they have a noticeable jump in curvature
• the gradient domain extension