feat(xhr): add request and response hook API

[adrums86]

Description

This PR would add xhr request and response hooks via an onRequest(callback) and onResponse(callback) API. The user can add as many unique hook callbacks as they want, and they will be called in the order they were added before the request and after the response is received respectively. The user can un-register these callbacks via the offRequest(callback) and offResponse(callback) API. The callback functions can take the following parameters:

• onRequest callbacks will pass the xhr request Object to the callback.
• onResponse callbacks will pass the xhr request, error, and response Objects to the callback in that order.

In addition, the user can use both global videojs.Vhs and player player.tech().xhr scoped API functions to add these hooks, where player hooks will override any global hooks.

Note: onRequest hooks are called after the beforeRequest function, so be aware that these hooks may further modify request options passed through that function.

Specific Changes proposed

Adding API functions to both Vhs and the VhsHandler for adding and removing unique xhr request and response hooks, passing those hooks to the xhr module, then calling them in the order they were added before an xhr request and in the response callback respectively.

Requirements Checklist

• Feature implemented / Bug fixed
• If necessary, more likely in a feature request than a bug fix
  • Unit Tests updated or fixed
  • Docs/guides updated
  • Example created (starter template on JSBin)
• Reviewed by Two Core Contributors

[codecov]

Codecov Report

Merging #1393 (e56d103) into main (bdd842a) will increase coverage by 0.04%.
The diff coverage is 95.74%.

@@            Coverage Diff             @@
##             main    #1393      +/-   ##
==========================================
+ Coverage   85.40%   85.45%   +0.04%     
==========================================
  Files          40       40              
  Lines        9963    10010      +47     
  Branches     2308     2317       +9     
==========================================
+ Hits         8509     8554      +45     
- Misses       1454     1456       +2     

Impacted Files	Coverage Δ
src/videojs-http-streaming.js	90.96% <94.73%> (+0.32%)	⬆️
src/xhr.js	100.00% <100.00%> (ø)

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[gkatsev]

A couple minor points.

I think my main question is whether these new methods should be namespaced on the xhr object itself. The main reason is that I think it'll reduce confusion in the future when VHS gets fetch support. So, people won't expect these to work when fetch is enabled.

[dzianis-dashkevich]

I thought about this kind of simplification

xhr._requestHooksSet = new Set();
xhr._responseHooksSet = new Set();

const addOnRequestHook = (callback) => xhr._requestHooksSet.add(callback);
const addOnResponseHook = (callback) => xhr._responseHooksSet.add(callback);

const removeOnRequestHook = (callback) => xhr._requestHooksSet.delete(callback);
const removeOnResponseHook = (callback) => xhr._responseHooksSet.delete(callback);

but then I realized that those 2 XHRs are not the same pointers...

LGTM!

[adrums86]

@gkatsev I totally agree regarding namespacing these to the xhr object to separate the hooks from fetch. Update incoming.

[adrums86]

@gkatsev and @misteroneill the namespace changes are pushed. Another quick look would be appreciated before merging. Thanks!

[misteroneill]