Store Greaselion extensions in user data dir and delete on exit

[emerick]

Resolves brave/brave-browser#12264
Resolves brave/brave-browser#12350

Previously we were unpacking the Greaselion extensions into a temporary directory not under our control. Those extensions were sometimes being deleted mid-session, which led to our translations not being found. In addition, the extensions weren't being deleted on service exit. This PR addresses both of those issues.

Submitter Checklist:

• Submitted a ticket for my issue if one did not already exist.
• Used Github auto-closing keywords in the commit message.
• Added/updated tests for this change (for new code or code which already has tests).
• Verified that these changes build without errors on
  • Android
  • iOS
  • Linux
  • macOS
  • Windows
• Verified that these changes pass automated tests (unit, browser, security tests) on
  • iOS
  • Linux
  • macOS
  • Windows
• Verified that all lint errors/warnings are resolved (npm run lint, npm run gn_check)
• Ran git rebase master (if needed).
• Ran git rebase -i to squash commits (if needed).
• Tagged reviewers and labelled the pull request as needed.
• Requested a security/privacy review as needed.
• Added appropriate QA labels (QA/Yes or QA/No) to the associated issue
• Added appropriate release note labels (release-notes/include or release-notes/exclude) to the associated issue
• Public documentation has been updated as necessary. For instance:
  • https://github.com/brave/brave-browser/wiki/Deviations-from-Chromium-(features-we-disable-or-remove)
  • https://github.com/brave/brave-browser/wiki/Proxy-redirected-URLs
  • https://github.com/brave/brave-browser/wiki/Fingerprinting-Protections
  • https://github.com/brave/brave-browser/wiki/Brave%E2%80%99s-Use-of-Referral-Codes
  • https://github.com/brave/brave-browser/wiki/Custom-Headers
  • https://github.com/brave/brave-browser/wiki/Web-compatibility-issues-with-tracking-protection
  • https://github.com/brave/brave-browser/wiki/QA-Guide

Test Plan:

• Clean profile
• Launch browser
• Visit https://github.com/brave/brave-core/commits/master or a similar Rewards media publisher that supports inline tips
• Verify that Tip button is inserted and that "Tip" text appears

I recommend trying this many times in various tabs. We should also test closing the tab and then restoring it with Ctrl+Shift+T. Can also test with various Rewards media publishers.

Reviewer Checklist:

• New files have MPL-2.0 license header.
• Request a security/privacy review as needed.
• Adequate test coverage exists to prevent regressions
• Verify test plan is specified in PR before merging to source

After-merge Checklist:

• The associated issue milestone is set to the smallest version that the
  changes has landed on.
• All relevant documentation has been updated.

[LaurenWags]

Verified using

Brave	1.19.13 Chromium: 87.0.4280.60 (Official Build) nightly (x86_64)
Revision	12697cfeb273d7de95cf9b18350d2c457f58224c-refs/branch-heads/4280@{#1352}
OS	macOS Version 10.14.6 (Build 18G6042)

Verified test plan from #7141 (comment)

Opened multiple tabs w/ in-line tip buttons. Examples:

• https://twitter.com/emerick, https://twitter.com/bravelaurenwags
• Upgrade from Chromium 87.0.4280.47 to Chromium 87.0.4280.49. brave-browser#12527 and other issue links
• https://github.com/brave/brave-core/commits/master
• 12691: Improve the PR checklist. #7140 and other PR links
• https://www.reddit.com/user/alex_the_brave, https://www.reddit.com/user/cryptojennie
• https://old.reddit.com/
• https://www.reddit.com/r/brave_browser/ and other subreddit links

Navigated thru the various pages to confirm "Tip" text and button were displayed.
Opened new pages via context menu and confirmed when page loaded the "Tip" text and button were displayed.
Closed tabs and reopened using cmd+shift+T and confirmed when page loaded the "Tip" text and button were displayed.
Left various pages as active and then closed/reopened the browser. On relaunch pages generally showed the "Tip" text and button, except for Twitter pages. This is logged with brave/brave-browser#11825. Confirmed reloading a tab that was left over from previous session showed the "Tip" text and button once page loaded.