🐛 Work around pdf-core expecting padded tags

The `scriptTag` and `langSysTag` properties in the shape options are
expected by `pdf-core` to be 4-character tags. Tags that are shorter
than 4 characters won't be recognized correctly.

This commit adds padding to these tags to ensure they are 4 characters
long, which is a workaround for the current behavior of `pdf-core`.

An example for setting the `language` property to select alternative
glyphs is added to the `examples/text.ts`.

Author: ralfstx

examples/text.ts

@@ -97,6 +97,8 @@ const document = {
           fontKerning: 'none',
           fontVariantLigatures: 'none',
         }),
+        text([text('Cyrillic default: '), text('бгдпт', { fontStyle: 'italic' })]),
+        text([text('Serbian: '), text('бгдпт', { fontStyle: 'italic', language: 'sr' })]),
       ],
       { margin: { y: 10 } },
     ),

src/text.ts

@@ -304,8 +304,9 @@ export function buildShapeOptions(
   const hasLangSysTag = langSysTag != null;
   if (!hasFeatures && !hasScriptTag && !hasLangSysTag) return undefined;
   return {
-    ...(hasScriptTag ? { scriptTag } : undefined),
-    ...(hasLangSysTag ? { langSysTag } : undefined),
+    // TODO: workaround for pdf-core expecting 4-character tags. Remove padding once that is fixed.
+    ...(hasScriptTag ? { scriptTag: scriptTag.padEnd(4, ' ') } : undefined),
+    ...(hasLangSysTag ? { langSysTag: langSysTag.padEnd(4, ' ') } : undefined),
     ...(hasFeatures ? { features } : undefined),
   };
 }