tools, docs: fix stability index isssues

[vsemozhetbyt]

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• commit message follows commit guidelines

Change 1: do not autolink in doc stability section

Currently, stability index descriptions in documentation.html contain links to their very section which is redundant. This commit prevents tools/doc/html.js from adding this links.

Screenshots of "before" and "after" states:

Before:

After:

Change 2: do not add void wrapping elements to docs

Currently, all the TOC links are wrapped in span elements with class according to stability index of their sections. However, most doc sections have not any stability index, so these spans have useless class stability_undefined. This commit prevents tools/doc/html.js from wrapping TOC links in useless spans.

Screenshots of "before" and "after" states (no visible difference):

Before:

After:

This PR eliminates 4402 useless elements in docs and reduces doc size by ~ 176 KB.

[BridgeAR]

LGTM but I suggest to use a shorter version.

[BridgeAR]

I suggest to change this to something like:

const link = filename === 'documentation' &&
  heading && heading.text === 'Stability Index' ?
    `${prefix} ${number}` :
    '<a href="documentation.html#documentation_stability_index">' +
      `${prefix} ${number}</a>`;
token.text = `<div class="api_stability api_stability_${number}">` +
  `${link}${explication}</div>`
    .replace(/\n/g, ' ');

It is just a bit shorter due to having less repetition.

[BridgeAR]

The same as above.

[vsemozhetbyt]

I've reduced diff and repetitions, PTAL.

CI-lite: https://ci.nodejs.org/job/node-test-pull-request-lite/711/

[vsemozhetbyt]

Landed in 2773de5
Thank you for the reviews.