Auto merge of #18355 - servo:no-fmt, r=emilio

Reduce usage of fmt in serialization and error reporting

`format!` and `write!` create a somewhat-heavyweight `Formatting` struct and use dynamic dispatch to call into impls of `Dispaly` and related traits. The former also allocates an intermediate string that is sometimes unnecessary.

I started looking into this from https://bugzilla.mozilla.org/show_bug.cgi?id=1355599, but I expect the impact there will be small to insignificant. It might be a slightly less so on parsing (error reporting).

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tests/wpt/mozilla/meta/MANIFEST.json

@@ -26530,7 +26530,7 @@
    "testharness"
   ],
   "mozilla/calc.html": [
-   "5b3ea33205a9f2404bd6976a2c7f6fc451be8e96",
+   "4f65929cacf623da2d3e310a6663d6165a1b0cdc",
    "testharness"
   ],
   "mozilla/canvas.initial.reset.2dstate.html": [

tests/wpt/mozilla/tests/mozilla/calc.html

@@ -42,7 +42,7 @@ var widthTests = [
     ['calc(10px + 10em - 10px)', 'calc(10em + 0px)', '160px'],
 
     // Fold absolute units
-    ['calc(1px + 1pt + 1pc + 1in + 1cm + 1mm)', 'calc(155.91666666666666px)', '155.91666666666666px'],
+    ['calc(96px + 72pt + 6pc + 1in + 2.54cm + 25.4mm)', 'calc(576px)', '576px'],
 
     // Alphabetical order
     ['calc(0ch + 0px + 0pt + 0pc + 0in + 0cm + 0mm + 0rem + 0em + 0ex + 0% + 0vw + 0vh + 0vmin + 0vmax)',