Match whole words when bolding member names in MDN comments - #2576

The MDN comment generator bolds the first regex match of the member name, but the pattern has no word boundaries, so short names get matched inside other words. The current baselines ship comments like:

- The DOMPointReadOnl**`y`** interface's y property holds the vertical coordinate ...
+ The DOMPointReadOnly interface's **`y`** property holds the vertical coordinate ...

The same thing happens for HTMLImageElement.y and SVGMaskElement.y ("read-onl**y** y property"), for Window.top and the global top ("**topmost window") and for TextEvent.initTextEvent ("initTextEvent**Event()").

This adds \b around the name in the regex, in line with the space-delimited matching suggested in the #2171 review. Interface.name and name() matches still work. "topmost" and MDN's "initTextEventEvent()" typo have no standalone match, so those two summaries are now left unbolded. Only these comment lines change in the dom and worker baselines.

Ran:

• npm run generate, then npm test: pass
• npx tsgo: pass

Checked:

• With the regenerated baselines and the old regex, node ./src/test.ts fails on the DOMPointReadOnly.y comment in dom.generated.d.ts.