Updated spinner animation on tab loads

[lucidNTR]

Original title: as a user i want to see modern looking spinner animation on tab loads #7779 (comment)

test plan:

#8160 (comment)

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• Did you search for similar issues before submitting this one?
  yes

• Describe the issue you encountered:
  the loader spinner on tabs looks outdated and should be replaced

• Platform (Win7, 8, 10? macOS? Linux distro?):
  all

• Brave Version (revision SHA):
  latest master 6f9a4f2

• Steps to reproduce:
  1.open tab
  2.enter http:// url
  3.press enter

• Actual result:
  the loading spinner looks old

• Expected result:
  modern looking loader that fits with rest of UI style

• Will the steps above reproduce in a fresh profile? If not what other info can be added?
  yes

• Is this an issue in the currently released version?
  yes

• Can this issue be consistently reproduced?
  yes

[lucidNTR]

I implemented a new style proposal, PR follows...