Replace modal window.history guard with state.history sentinel (#90776)

[WojtekBoman]

Explanation of Change

Moves shouldHandleNavigationBack modals off the direct window.history.pushState hack onto a react-navigation state.history sentinel (TOGGLE_MODAL_WITH_HISTORY), mirroring SidePanel. The router consumes the sentinel on forward navigation so useLinking replaces instead of stacking — removing the orphaned entry that caused the double-Back (#90776). Adds useSyncModalWithHistory; deletes the legacy guards.

Fixed Issues

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PROPOSAL:

Tests

1. Sign in with an account that has no workspaces and note the current URL.
2. Open the Floating Action Button (FAB) → Create workspace → confirm.
3. Press the browser Back button once.
4. Verify that you return to the pre-Workspaces screen with a single Back press (previously it took two).
5. Open the FAB again and press browser Back without selecting anything.
6. Verify that the popover just closes and the page/URL is unchanged.
7. From the new screen reached in step 2, use the in-app back/close button.
8. Verify that it still returns to the originating page.
9. Open another shouldHandleNavigationBack flow (e.g. a value/date picker or a ConfirmModal that routes onward), then a second modal on top of it, and press browser Back.
10. Verify that the modals close one Back press at a time (the inner one first), and that a plain modal still closes via Esc / click-outside / Back with no stranded history entry.
11. With a modal open, resize the browser window between narrow (mWeb) and wide layouts.
12. Verify that the modal stays open and no extra Back press is stranded.
13. Verify that no errors appear in the JS console.

Offline tests

N/A — these changes only affect navigation/browser-history state and do not involve API calls or Onyx data.

QA Steps

Same as tests.

• Verify that no errors appear in the JS console

PR Author Checklist

• I linked the correct issue in the ### Fixed Issues section above
• I wrote clear testing steps that cover the changes made in this PR
  • I added steps for local testing in the Tests section
  • I added steps for the expected offline behavior in the Offline steps section
  • I added steps for Staging and/or Production testing in the QA steps section
  • I added steps to cover failure scenarios (i.e. verify an input displays the correct error message if the entered data is not correct)
  • I turned off my network connection and tested it while offline to ensure it matches the expected behavior (i.e. verify the default avatar icon is displayed if app is offline)
  • I tested this PR with a High Traffic account against the staging or production API to ensure there are no regressions (e.g. long loading states that impact usability).
• I included screenshots or videos for tests on all platforms
• I ran the tests on all platforms & verified they passed on:
  • Android: Native
  • Android: mWeb Chrome
  • iOS: Native
  • iOS: mWeb Safari
  • MacOS: Chrome / Safari
• I verified there are no console errors (if there's a console error not related to the PR, report it or open an issue for it to be fixed)
• I followed proper code patterns (see Reviewing the code)
  • I verified that any callback methods that were added or modified are named for what the method does and never what callback they handle (i.e. toggleReport and not onIconClick)
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  • I verified that any new or modified comments were clear, correct English, and explained "why" the code was doing something instead of only explaining "what" the code was doing.
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• If a new code pattern is added I verified it was agreed to be used by multiple Expensify engineers
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• I tested other components that can be impacted by my changes (i.e. if the PR modifies a shared library or component like Avatar, I verified the components using Avatar are working as expected)
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• I verified any variables that can be defined as constants (ie. in CONST.ts or at the top of the file that uses the constant) are defined as such
• I verified that if a function's arguments changed that all usages have also been updated correctly
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  • The file has a description of what it does and/or why is needed at the top of the file if the code is not self explanatory
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  • The style can't be created with an existing StyleUtils function (i.e. StyleUtils.getBackgroundAndBorderStyle(theme.componentBG))
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• If the PR modifies code that runs when editing or sending messages, I tested and verified there is no unexpected behavior for all supported markdown - URLs, single line code, code blocks, quotes, headings, bold, strikethrough, and italic.
• If the PR modifies a generic component, I tested and verified that those changes do not break usages of that component in the rest of the App (i.e. if a shared library or component like Avatar is modified, I verified that Avatar is working as expected in all cases)
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• If the PR modifies a component or page that can be accessed by a direct deeplink, I verified that the code functions as expected when the deeplink is used - from a logged in and logged out account.
• If the PR modifies the UI (e.g. new buttons, new UI components, changing the padding/spacing/sizing, moving components, etc) or modifies the form input styles:
  • I verified that all the inputs inside a form are aligned with each other.
  • I added Design label and/or tagged @Expensify/design so the design team can review the changes.
• If a new page is added, I verified it's using the ScrollView component to make it scrollable when more elements are added to the page.
• I added unit tests for any new feature or bug fix in this PR to help automatically prevent regressions in this user flow.
• If the main branch was merged into this PR after a review, I tested again and verified the outcome was still expected according to the Test steps.

Screenshots/Videos

Android: Native

Android: mWeb Chrome

iOS: Native

iOS: mWeb Safari

MacOS: Chrome / Safari