katex [nfc]: Consolidate where we cancel out ambient text styles

In the inline-math case, we're about to pass the actual ambient text
style, which may have italic, strikethrough, bold, or link
formatting. Consolidate the code that overrides each of those, so
that it reads as intentional, and add TODOs for overrides that we
might not want to keep.

Author: chrisbobbe

lib/widgets/katex.dart

@@ -10,12 +10,28 @@ import 'content.dart';
 
 /// Creates a base text style for rendering KaTeX content.
 ///
-/// This applies the CSS styles defined in .katex class in katex.scss :
+/// This cancels out some attributes that may be ambient from Zulip content
+/// (italic, bold, etc.)
+/// and applies the CSS styles defined in .katex class in katex.scss :
 ///   https://github.com/KaTeX/KaTeX/blob/613c3da8/src/styles/katex.scss#L13-L15
 ///
 /// Requires the [style.fontSize] to be non-null.
-TextStyle mkBaseKatexTextStyle(TextStyle style) {
+TextStyle mkBaseKatexTextStyle(TextStyle style, Color baseColor) {
   return style.copyWith(
+    ////// Overrides of our own styles:
+
+    // Bold formatting is removed below by setting FontWeight.normal…
+    // Just for completeness, remove "wght", but it wouldn't do anything anyway
+    // since KaTeX_Main is not a variable-weight font.
+    fontVariations: [],
+    // Remove link color, but
+    // TODO(design) do we want to do that?
+    color: baseColor,
+    // italic and strikethrough are removed below, but
+    // TODO(design) do we want to remove a strikethrough?
+
+    ////// From the .katex class in katex.scss:
+
     fontSize: style.fontSize! * 1.21,
     fontFamily: 'KaTeX_Main',
     height: 1.2,
@@ -45,8 +61,8 @@ class KatexWidget extends StatelessWidget {
     return Directionality(
       textDirection: TextDirection.ltr,
       child: DefaultTextStyle(
-        style: mkBaseKatexTextStyle(textStyle).copyWith(
-          color: ContentTheme.of(context).textStylePlainParagraph.color),
+        style: mkBaseKatexTextStyle(textStyle,
+          ContentTheme.of(context).textStylePlainParagraph.color!),
         child: widget));
   }
 }