Implement Reddit inline tipping for flat menu

[jasonrsadler]

Description

Implement Reddit inline tipping for menu that appears at bottom of posts/comments (flat menu)

New feature request

[GeetaSarvadnya]

Verification passed on

Brave	0.68.106 Chromium: 76.0.3809.62 (Official Build) dev (64-bit)
Revision	7b77856b3aa34d72f246d12340fc1ded8b2c0e83-refs/branch-heads/3809@{#798}
OS	Windows 10 OS Version 1803 (Build 17134.523)

• Verified the test plan from Reddit inline tips link on post menu will now appear brave-core#2665
  • Verified the inline tip link for Reddit posts

• Verified Reddit pubs displayed in tips panel after sending tips
  

• Verified user can send a tip by clicking on inline tip link in Reddit posts

• Verified Tip link is not shown when Reddit checkbox is unchecked in Tips panel in brave://rewards

• Verified Tip link is not shown when brave://rewards is not enabled

Verification passed on

Brave	0.68.114 Chromium: 76.0.3809.87 (Official Build) beta (64-bit)
Revision	111fe1e15d5ced26080a7dc239bcfe70f6c49aad-refs/branch-heads/3809@{#967}
OS	Ubuntu 18.04 LTS

Verified the test plan from brave/brave-core#2665

• Verified the inline tip link for Reddit posts
  
• Verified Reddit pubs displayed in tips panel after sending tips
  
  • Verified user can send a tip by clicking on inline tip link in Reddit posts
  • Verified Tip link is not shown when Reddit checkbox is unchecked in Tips panel in brave://rewards
  • Verified Tip link is not shown when brave://rewards is not enabled

Verified passed with

Brave	0.68.119 Chromium: 76.0.3809.87 (Official Build) beta (64-bit)
Revision	111fe1e15d5ced26080a7dc239bcfe70f6c49aad-refs/branch-heads/3809@{#967}
OS	Mac OS X

• Verified the test plan from Reddit inline tips link on post menu will now appear brave-core#2665
• Verified Reddit pubs displayed in tips panel after sending tips
• Verified user can send a tip by clicking on inline tip link in Reddit posts
• Verified Tip button is not shown when Reddit checkbox is unchecked in Tips panel in brave://rewards however I had to refresh the page. This shouldn't be the case, logged disabling content level tips for Reddit doesn't remove tip button from in-line menu until page refresh #5551 - Verified Tip button is not shown when brave://rewards is not enabled
• logged inline 'Tip' text does not change color on hover on reddit  #5702 - tip text does not change color on hover