Update macOS postinstall script to properly build executable paths

[bsclifton]

Update postinstall script to properly build executable paths (install path + user data dir name)

Fixes brave/brave-browser#4600

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
  • Windows
  • macOS
  • Linux
• Verified that these changes pass automated tests (npm test brave_unit_tests && npm test brave_browser_tests && npm run test-security) on
  • Windows
  • macOS
  • Linux
• Verified that all lint errors/warnings are resolved (npm run lint)
• Ran git rebase master (if needed).
• Ran git rebase -i to squash commits (if needed).
• Tagged reviewers and labelled the pull request as needed.
• Request a security/privacy review as needed.
• Add appropriate QA labels (QA/Yes or QA/No) to include the closed issue in milestone
• 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-Protection-Mode
  • 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:

1. Download the PKG file (message @bsclifton if unsure where/how to download)
2. Rename it in a format like Brave Browser Dev-BSC123.pkg (where BSC123 is your referral promo code)
3. Run the installer
4. promoCode file should be created in ~/Library/BraveSoftware/Brave-Browser-Dev/promoCode
5. Open file and verify contents are BSC123 (or whatever your promo code was)

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.

[bsclifton]

Gonna let PR builder run so I can get the PKG file and give it a go 😄

[bsclifton]

OK finally got this building properly- testing it out now

[bsclifton]

Ready for review! I tested this out and it worked great. You can download the .pkg file from build performed with https://staging.ci.brave.com/job/brave-core-build-pr/job/PR-2549/20/

I downloaded/tested using the binaries from https://staging.ci.brave.com/job/brave-core-build-pr/job/PR-2549/18/ which are identical minus some comments which I forgot to delete from the postinstall script

You can verify the actions taken using the Installer Log menu item (and changing filter to Show All Logs):

[emerick]

Thanks for picking this up @bsclifton, it looks really good! I had one minor comment, might be nothing.

[bsclifton]

quick note: going to stop the CI for this, as the change I made only affects the postinstall script which is not tested as part of CI (also, default builds have signing skipped, which omits the creation of the .pkg file)

[emerick]

LGTM