ui: Reduce icons stroke width (#36361)

After redesigning all Zed icons
(https://github.com/zed-industries/zed/pull/35856), it felt like using
1.5 for stroke width didn't really flow well with the default typeface
default font weight. Reducing it to 1.2 makes the UI much sharper, less
burry, and more cohesive overall.

Release Notes:

- N/A

assets/icons/debug_detach.svg

@@ -1 +1 @@
-<svg xmlns="http://www.w3.org/2000/svg" width="16" height="16" fill="none"><g stroke="#000" stroke-linecap="round" stroke-linejoin="round" stroke-width="1.5" clip-path="url(#a)"><path d="m13 3 2-2M1 15l2-2M4.202 13.53a1.598 1.598 0 0 0 2.266 0L8 11.997 4.003 8 2.47 9.532a1.6 1.6 0 0 0 0 2.265l1.732 1.733ZM5 9l1.5-1.5M7 11l1.5-1.5M8 4.003 11.997 8l1.533-1.532a1.599 1.599 0 0 0 0-2.266L11.798 2.47a1.598 1.598 0 0 0-2.266 0L8 4.003Z"/></g><defs><clipPath id="a"><path fill="#fff" d="M0 0h16v16H0z"/></clipPath></defs></svg>
+<svg xmlns="http://www.w3.org/2000/svg" width="16" height="16" fill="none"><g stroke="#000" stroke-linecap="round" stroke-linejoin="round" stroke-width="1.2" clip-path="url(#a)"><path d="m13 3 2-2M1 15l2-2M4.202 13.53a1.598 1.598 0 0 0 2.266 0L8 11.997 4.003 8 2.47 9.532a1.6 1.6 0 0 0 0 2.265l1.732 1.733ZM5 9l1.5-1.5M7 11l1.5-1.5M8 4.003 11.997 8l1.533-1.532a1.599 1.599 0 0 0 0-2.266L11.798 2.47a1.598 1.598 0 0 0-2.266 0L8 4.003Z"/></g><defs><clipPath id="a"><path fill="#fff" d="M0 0h16v16H0z"/></clipPath></defs></svg>