Update Twitter Greaselion script to use locales directory for localizations

[emerick]

When brave/brave-core#6683 is merged, update our Twitter Greaselion script to use the locales_ directory for localizations. Currently, the text for our UI is hardcoded directly into the Twitter script.

[LaurenWags]

@emerick since this one is marked QA/Yes could we get a test plan for this? if manual QA is not needed, let's label as QA/No 👍 labeling QA/Blocked for now until we sort this out.

[emerick]

@LaurenWags I updated the test plan in the PR, give me a holler if anything doesn't make sense with it.

[LaurenWags]

Verified passed with

Brave | 1.17.45 Chromium: 86.0.4240.99 (Official Build) dev (x86_64)
-- | --
Revision | 002668237e13d38aabd6d11c2d216dd22b736ff2-refs/branch-heads/4240@{#1229}
OS | macOS Version 10.14.6 (Build 18G3020)

Verified test plan from brave/brave-core#6683. Note - each OS may have a slightly different method to getting Brave to display in a different language (as noted in the steps). Here are the steps I followed - modified from the PR after discussion with @emerick:

• Clean profile
• Launch browser
• Enable Rewards and restart browser
• Visit twitter.com/emerick
• Verify that inline tips appear with US localizations

• Locate the Greaselion _locales directory for Twitter (on macOS: ⁨Library⁩ ▸ ⁨Application Support⁩ ▸ ⁨BraveSoftware⁩ ▸ ⁨Brave-Browser-Dev⁩ ▸ ⁨afalakplffnnnlkncjhbmahjfjhmlkal⁩ ▸ ⁨1.0.32⁩ ▸ ⁨1⁩ ▸ ⁨scripts⁩ ▸ ⁨brave_rewards⁩ ▸ ⁨publisher⁩ ▸ ⁨twitter⁩ ▸ ⁨_locales⁩)
• Copy the en_US directory and rename de
• Edit the message fields in de/messages.json to distinguish them from US localizations.

• Open browser Settings
• Search for Language
• Click "Add Languages"
• Select "German - Deutsch" and click "Add"
• Click three dots on "German" and select "Move to top"
• Open OS settings, change OS language to German
• Relaunch Brave
• Visit twitter.com/emerick again
• Verify that inline tips appear with German localizations

Verification passed on

Brave	1.17.59 Chromium: 86.0.4240.183 (Official Build) dev (64-bit)
Revision	0b568b034b8f7994697cb341eeca5979b84151cc-refs/branch-heads/4240@{#1374}
OS	Ubuntu 18.04 LTS

Verified test plan from brave/brave-core#6683.
Used PL locale

---

Verification passed on

Brave	1.17.68 Chromium: 87.0.4280.49 (Official Build) (64-bit)
Revision	f77f85899646b42a1d3c8ff36794e00becab9171-refs/branch-heads/4280@{#1115}
OS	Windows 7 Service Pack 1 (Build 7601.24544)

Verified test plan from brave/brave-core#6683.

US locale:

PL locale: