Set tooltip texts for toggle button on vertical tabs

[sangwoo108]

Resolves brave/brave-browser#29593

• While expanded

• While floating

• While minimized

Submitter Checklist:

• I confirm that no security/privacy review is needed, or that I have requested one
• There is a ticket for my issue
• Used Github auto-closing keywords in the PR description above
• Wrote a good PR/commit description
• Squashed any review feedback or "fixup" commits before merge, so that history is a record of what happened in the repo, not your PR
• Added appropriate labels (QA/Yes or QA/No; release-notes/include or release-notes/exclude; OS/...) to the associated issue
• Checked the PR locally:
  • npm run test -- brave_browser_tests, npm run test -- brave_unit_tests wiki
  • npm run lint, npm run presubmit wiki, npm run gn_check, npm run tslint
• Ran git rebase master (if needed)

Reviewer Checklist:

• A security review is not needed, or a link to one is included in the PR description
• New files have MPL-2.0 license header
• Adequate test coverage exists to prevent regressions
• Major classes, functions and non-trivial code blocks are well-commented
• Changes in component dependencies are properly reflected in gn
• Code follows the style guide
• Test plan is specified in PR before merging

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, 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-Exceptions-in-Brave
  • https://github.com/brave/brave-browser/wiki/QA-Guide
  • https://github.com/brave/brave-browser/wiki/P3A

Test Plan:

• Enable vertical tabs
• Move mouse on the toggle button on the top of vertical tab strip.
• See if tooltip texts aren't empty

[stephendonner]

Verified PASSED using

Brave	1.52.35 Chromium: 112.0.5615.49 (Official Build) nightly (x86_64)
Revision	bd2a7bcb881c11e8cfe3078709382934e3916914-refs/branch-heads/5615@{#936}
OS	macOS Version 13.4 (Build 22F5027f)

Steps:

1. install 1.52.35
2. launch Brave
3. loaded mozilla.com
4. loaded https://en.wikipedia.org/wiki/Latin_alphabet
5. context-clicked on the 1st tab
6. chose Use vertical tabs
7. hovered over (and clicked on) the "sidebar"/"side panel" button, to expand
8. confirmed the tooltip reads Minimize Tabs
9. pinned tabs
10. hovered over the button again
11. confirmed the tooltip reads Minimize Tabs
12. clicked again to minimize
13. confirmed the tooltip reads Expand Tabs

while expanded, Minimize Tabs	while floating, Minimize Tabs	while minimized, Expand Tabs