[Brave News]: Update Subscribe Button Icon

[fallaciousreasoning]

We have a new subscribe button icon we should use thanks to @martin-c0des.

https://www.figma.com/file/w13WS9lovJubjbSjtK1fVo/Brave-Desktop---Add-to-Brave-News?node-id=129%3A13678&t=R4BQ7wBZ9LhXjZnj-0#313822908

[fallaciousreasoning]

Hey @martin-c0des, I've just been updating the icon and there isn't heaps to distinguish between the subscribed & unsubscribed states:

Unsubscribed

Subscribed

[fallaciousreasoning]

I had a dig into the code, and it looks like we were doing something to reduce the contrast, to make the colors the same as the other icons. Even with that disabled it's kinda hard to tell the icon has changed:

No contrast reduction:

[kjozwiak]

We'll be uplifted the above into the 1.46.x maintenance release via brave/brave-core#16143 once the initial 1.46.x build goes out. Verification will be completed on 1.46.x.

[kjozwiak]

The above requires 1.46.139 or higher for 1.46.x verification 👍

[GeetaSarvadnya]

Verification PASSED on

Brave | 1.46.141 Chromium: 108.0.5359.99 (Official Build) (64-bit)
-- | --
Revision | 410951fc34bb4b2cbf182231f9f779efaafaf682-refs/branch-heads/5359_71@{#9}
OS | Windows 10 Version 21H2 (Build 19044.2251)

Steps:

1. installed 1.48.13
2. launched Brave
3. set brave://flags/#brave-news-subscribe-button to Enabled
4. clicked Relaunch
5. loaded planet.mozilla.org
6. changed modes and theme
7. hovered over the buttons

Confirmed new RSS icon across the following:

Dark mode	Dark mode, hover	Light mode	Light mode, hover	purple theme	purple theme, hover

[btlechowski]

Verification PASSED on

Brave	1.46.141 Chromium: 108.0.5359.99 (Official Build) (64-bit)
Revision	410951fc34bb4b2cbf182231f9f779efaafaf682-refs/branch-heads/5359_71@{#9}
OS	Ubuntu 18.04 LTS

Steps:

1. installed 1.46.x
2. launched Brave
3. set brave://flags/#brave-news-subscribe-button to Enabled
4. clicked Relaunch
5. loaded planet.mozilla.org
6. changed modes and theme
7. verified subscribed/unsubscribed/hover states

Dark mode

unsubscribed

unsubscribed - hover

subscribed

subscribed - hover

Light mode

unsubscribed

unsubscribed - hover

subscribed

subscribed - hover

[stephendonner]

Verified PASSED using

Brave	1.46.141 Chromium: 108.0.5359.99 (Official Build) (x86_64)
Revision	410951fc34bb4b2cbf182231f9f779efaafaf682-refs/branch-heads/5359_71@{#9}
OS	macOS Version 13.1 (Build 22C65)

Steps:

1. installed 1.46.141
2. launched Brave
3. opened brave://flags
4. set brave://flags/#brave-news-subscribe-button to Enabled
5. clicked Relaunch
6. loaded planet.mozilla.org
7. verified subscribed/unsubscribed/hover states

Light mode

unsubscribed	unsubscribed, hover	subscribed	subscribed, hover

Dark mode

unsubscribed	unsubscribed, hover	subscribed	subscribed, hover