Formalize process for browser checks and create relevant files

The following discussion from gitlab-ce!24017 should be addressed:

• @pslaughter started a discussion: (+3 comments)

  @kushalpandya, thanks for this! I think it is a good idea to capture this on the DOM. However, I'm concerned about our code being peppered with browser checks:

  function initializingWombats() {
    if (isChrome || isFirefox) { 
      // ... 
    }
  
    if (!isIE11 && !isEdge) { 
      // ... 
    }
  }

  What if we strictly limit these browser checks in a single features.js?

  const { isIe, isEdge, isChrome, isFirefox } = gl.client;
  
  export const emojisLookGood = () => !isIe && !isEdge;
  export const tooltipsLookGood = () => isChrome || isFirefox;
  // ...

  WDYT?

/cc @kushalpandya @andr3