Update shadow layer bounds when tab's layer bounds changes

[sangwoo108]

When scrolling, tab's bounds doesn't change while the layer's bounds changes. In order to synchronize shadow_layer_'s bounds to it, we should layout it from OnLayerBoundsChanged().

Resolves brave/brave-browser#29791

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 tab strip
• Make as many tabs as you can scroll the scroll area
• Try scrolling the area
• Check if the shadow for the active tab is positioned well

[MadhaviSeelam]

Verification PASSED on Win 11 x64 using the following build(s):

Brave | 1.52.64 Chromium: 112.0.5615.165 (Official Build) nightly (64-bit)
-- | --
Revision | c262f36e6b1d711ee42d4fbe1343b49960593f18-refs/branch-heads/5615@{#1297}
OS | Windows 11 Version 22H2 (Build 22621.1555)

Verified using STR from #18111 (comment)

• Install 1.52.64

• launch Brave

• open brave://flags and enabled for #brave-vertical-tabs

• clicked Relaunch

• added few tabs in horizontal tab view

• open brave://settings/appearance

• toggled on Use vertical tabs under tabs section

• confirmed vertical tab view is enabled

• added few more tabs to vertical tab view

• scroll down to the last tab and scolled back up in the panel

• Confirmed no shadow/grey area shown in between tabs and inactive and active tabs are highlighted as expected

ex	ex