New Tab Page Grid alignment should be more dynamic

[petemill]

• Allow items to fill in gaps left by other items which are turned off
• Allow any item to fit next to any item, even if it occupies 2 rows (e.g. Branded Wallpaper Logo item, or Rewards item)

Test plan on brave/brave-core#4075 (Items 9 and 10)

[kjozwiak]

Verification PASSED on macOS 10.15.3 x64 using the following build:

Brave	1.3.108 Chromium: 79.0.3945.130 (Official Build) beta (64-bit)
Revision	e22de67c28798d98833a7137c0e22876237fc40a-refs/branch-heads/3945@{#1047}
OS	macOS Version 10.15.3 (Build 19D76)

• Verified cases 9 & 10 as per New Tab Page Grid alignment should be more dynamic #7884 (comment)

Different window sizes

Stats widget disabled

Clock widget disabled

Top Sites widget disabled

Other variations

Verification passed on

Brave	1.3.110 Chromium: 80.0.3987.78 (Official Build) (64-bit)
Revision	cb5aa81cb0a3a2c674b93bc7ffb34a86cd3b4802-refs/branch-heads/3987@{#752}
OS	Windows 10 OS Version 1803 (Build 17134.1006)

• Verified cases 9 & 10 as per New Tab Page Grid alignment should be more dynamic #7884 (comment)

Different window sizes

Stats widget disabled

Clock widget disabled

Top Sites widget disabled

Verification passed on

Brave	1.3.111 Chromium: 80.0.3987.85 (Official Build) (64-bit)
Revision	583b05dfa4ffc657f0f7c5cc13f53aa17c9a5bcf-refs/branch-heads/3987@{#791}
OS	Ubuntu 18.04 LTS

• Verified cases 9 & 10 as per New Tab Page Grid alignment should be more dynamic #7884 (comment)

Different window sizes

Stats widget disabled

Clock widget disabled

Top Sites widget disabled