Ship Material Symbols in the 20 optical-size cut

M3 draws icons at 20 dp from the optical size 20 cut, whose strokes stay as
heavy as the 24 dp design's instead of thinning with the glyph (styles.md
§ Icons, the optical size axis). The package only shipped the 24 cut, so every
20 px icon was a scaled-down 24 (core audit C16). bin/fetch-symbols now checks
out both cuts from the same commit of google/material-design-icons and writes
the new one to resources/svg/symbols/{outlined-20,filled-20}: 4,135 symbols
each, the same names and the same normalisation as the 24 cut.

Plan step 10; finding C16.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Qwx5USif3wFFmxtHg5U1g9

resources/svg/symbols/filled-20/question_exchange.svg

@@ -0,0 +1 @@
+<svg fill="currentColor" xmlns="http://www.w3.org/2000/svg" viewBox="0 -960 960 960"><path d="M480-48q-113 0-207.5-52.5T120-241v85q0 15-10.5 25.5T84-120q-15 0-25.5-10.5T48-156v-168q0-15 10.5-25.5T84-360h168q15 0 25.5 10.5T288-324q0 15-10.5 25.5T252-288h-77q48 76 128 122t177 46q141 0 242.5-94T838-445q2-15 12.5-25t25.5-10q15 0 26 10.5t9 24.5q-7 83-43 155.5t-94 126Q716-110 640.5-79T480-48Zm0-792q-141 0-242.5 94T122-515q-2 15-12.5 25T84-480q-15 0-26-10.5T49-515q7-83 43-155.5t94-126Q244-850 319.5-881T480-912q113 0 207.5 52.5T840-719v-85q0-15 10.5-25.5T876-840q15 0 25.5 10.5T912-804v168q0 15-10.5 25.5T876-600H708q-15 0-25.5-10.5T672-636q0-15 10.5-25.5T708-672h77q-48-76-128-122t-177-46Zm0 600q21 0 35.5-14.5T530-290q0-21-14.5-36T480-341q-21 0-35.5 14.5T430-291q0 21 14.5 36t35.5 15Zm78-247q24-23 41-47.5t17-60.5q0-57-39-91t-97-34q-40 0-71 16.5T358-655q-8 13-2.5 28t19.5 21q14 6 27.5-.5T426-625q11-12 24.5-19t29.5-7q28 0 46.5 15.5T545-594q0 23-16.5 42T493-514q-26 25-36 42t-12 43q-2 16 9 27t27 11q15 0 25-11.5t13-26.5q3-17 11.5-28.5T558-487Z"/></svg>