Part 2: Implement Animate for track lists on grid-template-{columns|rows}.

Based on https://bugzilla.mozilla.org/show_bug.cgi?id=1348519#c6 and
w3c/csswg-drafts#3201:

Currently grid-template-rows/columns interpolate “per computed value”, which
means that if the number of tracks differs, or any track changes to/from a
particular keyword value to any other value, or if a line name is added/removed
at any position, the entire track listing is interpolated as “discrete”.
But we "agree" with two more granular options:

1. Check interpolation type per track, rather than for the entire list, before
   falling back to discrete. I.e. a length-percentage track can animate between
   two values while an adjacent auto track flips discretely to min-content.
2. Allow discrete interpolation of line name changes independently of track
   sizes.

Besides, for the repeat() function, it's complicated to support interpolation
between different repeat types (i.e. auto-fill, auto-fit) and different repeat
counts, so we always fall-back to discrete if the first parameter of repeat()
is different.

Depends on D16339

Differential Revision: https://phabricator.services.mozilla.com/D16129

bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1348519
gecko-commit: bd4efc854419ae1643bfaeeedc67403703575ea0
gecko-integration-branch: central
gecko-reviewers: emilio

Author: BorisChiou

web-animations/animation-model/animation-types/property-list.js

@@ -679,18 +679,6 @@ const gCSSProperties = {
       { type: 'discrete', options: [ [ '". . a b" ". .a b"', 'none' ] ] }
     ]
   },
-  'grid-template-columns': {
-    // https://drafts.csswg.org/css-template/#grid-template-columns
-    types: [
-      { type: 'discrete', options: [ [ '1px', '5px' ] ] }
-    ]
-  },
-  'grid-template-rows': {
-    // https://drafts.csswg.org/css-template/#grid-template-rows
-    types: [
-      { type: 'discrete', options: [ [ '1px', '5px' ] ] }
-    ]
-  },
   'height': {
     // https://drafts.csswg.org/css21/visudet.html#propdef-height
     types: [