Update to UI and Framework Icons (#9468)

This is an update to 82 Zed UI and file_icons to improve icon legibility
and align contributed file_icons to the general icon system styling.
From review it appears they're 2px larger in width and height but gpui
render scaling is at play. The original icons were designed at 14x14 to
be viewed at that size, but the ui_font_size now controls this so
they've been updated to the default of 16x16 for optimum fidelity.

![CleanShot 2024-03-17 at 16 20
13@2x](https://github.com/zed-industries/zed/assets/1648941/4151c631-78e6-43a8-914f-37b00f43e130)

Release Notes:

- Updated various UI and file icons for consistency.

assets/icons/file_icons/chevron_down.svg

@@ -1,3 +1,3 @@
-<svg width="14" height="14" viewBox="0 0 14 14" fill="none" xmlns="http://www.w3.org/2000/svg">
-<path d="M3.63281 5.66406L6.99344 8.89844L10.3672 5.66406" stroke="black" stroke-width="1.25" stroke-linecap="round" stroke-linejoin="round"/>
+<svg width="16" height="16" viewBox="0 0 16 16" fill="none" xmlns="http://www.w3.org/2000/svg">
+<path d="M4.63281 6.66406L7.99344 9.89844L11.3672 6.66406" stroke="black" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round"/>
 </svg>