(core) Adding font options to the style picker

Summary:
Redesigning color picker:
- Single color palette (no light/dark switch)
- Ability to remove color (new empty button)

New font options in the color picker.
Font options are available on:
- Default cell style
- Conditional rules styles
- Choice/ChoiceList editor and token field
- Filters for Choice/ChoiceList columns

Design document:
https://www.figma.com/file/bRTsb47VIOVBfJPj0qF3C9/Grist-Updates?node-id=415%3A8135

Test Plan: new and updated tests

Reviewers: georgegevoian, alexmojaki

Reviewed By: georgegevoian, alexmojaki

Subscribers: alexmojaki

Differential Revision: https://phab.getgrist.com/D3335

app/client/ui2018/cssVars.ts

@@ -143,8 +143,27 @@ const cssInputFonts = `
   }
 `;
 
+// Font style classes used by style selector.
+const cssFontStyles = `
+  .font-italic {
+    font-style: italic;
+  }
+  .font-bold {
+    font-weight: 800;
+  }
+  .font-underline {
+    text-decoration: underline;
+  }
+  .font-strikethrough {
+    text-decoration: line-through;
+  }
+  .font-strikethrough.font-underline {
+    text-decoration: line-through underline;
+  }
+`;
+
 const cssVarsOnly = styled('div', cssColors + cssVars);
-const cssBodyVars = styled('div', cssFontParams + cssColors + cssVars + cssBorderBox + cssInputFonts);
+const cssBodyVars = styled('div', cssFontParams + cssColors + cssVars + cssBorderBox + cssInputFonts + cssFontStyles);
 
 const cssBody = styled('body', `
   margin: 0;