Resolved sans-serif font issue for firefox browser (#418)

The FireFox browser was throwing an error when using the default font
for canvas.

When the canvas text renderer tries to add the default font (fallback
font). However during the creation of the WebFont (line: 120
CanvasTextRenderer) it creates a FontFace which creates a family
property which is an empty string in FireFox. This is where we run into
problems because that empty string is used as a key later on.

I have resolved the issue by building in a fallback that in case the
family returns an empty string it falls back to the fontFamily property
of its super class.

src/core/text-rendering/TrFontManager.ts

@@ -46,6 +46,7 @@ function resolveFontToUse(
 
   for (const fontFamiles of familyMapsByPriority) {
     const fontFaces = fontFamiles[family];
+
     if (!fontFaces) {
       continue;
     }

src/core/text-rendering/font-face-types/TrFontFace.ts

@@ -154,7 +154,6 @@ export class TrFontFace extends EventEmitter {
         lineGap: metrics.lineGap / metrics.unitsPerEm,
       };
     }
-
     this.fontFamily = fontFamily;
     this.descriptors = {
       style: 'normal',

src/core/text-rendering/renderers/CanvasTextRenderer.ts

@@ -242,24 +242,22 @@ export class CanvasTextRenderer extends TextRenderer<CanvasTextRendererState> {
     // the `isFontFaceSupported` check)
     assertTruthy(fontFace instanceof WebTrFontFace);
 
+    const fontFamily = fontFace.fontFamily;
+
     // Add the font face to the document
     // Except for the 'sans-serif' font family, which the Renderer provides
     // as a special default fallback.
-    if (fontFace.fontFamily !== 'sans-serif') {
+    if (fontFamily !== 'sans-serif') {
       // @ts-expect-error `add()` method should be available from a FontFaceSet
       // eslint-disable-next-line @typescript-eslint/no-unsafe-call
       globalFontSet.add(fontFace.fontFace);
     }
 
-    const { fontFamilies } = this;
-    const familyName = fontFace.fontFace.family;
-
-    let faceSet = fontFamilies[familyName];
+    let faceSet = this.fontFamilies[fontFamily];
     if (!faceSet) {
       faceSet = new Set();
-      fontFamilies[familyName] = faceSet;
+      this.fontFamilies[fontFamily] = faceSet;
     }
-
     faceSet.add(fontFace);
   }
 
@@ -384,6 +382,7 @@ export class CanvasTextRenderer extends TextRenderer<CanvasTextRendererState> {
 
   loadFont = (state: CanvasTextRendererState): void => {
     const cssString = getFontCssString(state.props);
+
     const trFontFace = this.stage.fontManager.resolveFontFace(
       this.fontFamilyArray,
       state.props,