Log context when a parser fails to load

Previously this just put a bunch of `web-tree-sitter` errors in the console without telling you which thing failed. This is a marginal improvement.

src/wasm-tree-sitter-grammar.js

@@ -136,7 +136,12 @@ module.exports = class WASMTreeSitterGrammar {
   async getLanguage() {
     await parserInitPromise;
     if (!this._language) {
-      this._language = await Parser.Language.load(this.treeSitterGrammarPath);
+      try {
+        this._language = await Parser.Language.load(this.treeSitterGrammarPath);
+      } catch (err) {
+        console.error(`Error loading grammar for ${this.scopeName}; original error follows`);
+        throw err;
+      }
     }
 
     if (!this._queryFilesLoaded) {