Highlight special onclosetag logic for p and br

`Parser.ts` has special `onclosetag` logic for
[`p`](https://github.com/fb55/htmlparser2/blob/6445c32b05dc070049eeaaf201bfc123daca3d37/src/Parser.ts#L336)
and
[`br`](https://github.com/fb55/htmlparser2/blob/6445c32b05dc070049eeaaf201bfc123daca3d37/src/Parser.ts#L340) tags.

The updated tests in PR fb55#1046 were unable to expose any
behavioral differences, despite the different code paths
taken by the existing special logic. So I decided it would be
best to at least to clarify with an update to the existing
comment in the code, as well as by using the literal values
'p' and 'br' instead of the variable `name` (which is
guaranteed to have those values).

src/Parser.ts

@@ -334,14 +334,15 @@ export class Parser {
                     }
                 } else this.stack.length = pos;
             } else if (!this.options.xmlMode && name === "p") {
-                this.emitOpenTag(name);
+                // Implicit open before close
+                this.emitOpenTag("p");
                 this.closeCurrentTag(true);
             }
         } else if (!this.options.xmlMode && name === "br") {
-            // We can't go through `emitOpenTag` here, as `br` would be implicitly closed.
-            this.cbs.onopentagname?.(name);
-            this.cbs.onopentag?.(name, {}, true);
-            this.cbs.onclosetag?.(name, false);
+            // We can't use `emitOpenTag` for implicit open, as `br` would be implicitly closed.
+            this.cbs.onopentagname?.("br");
+            this.cbs.onopentag?.("br", {}, true);
+            this.cbs.onclosetag?.("br", false);
         }
 
         // Set `startIndex` for next node