#9209 Implement "unsaved" mods

[BLoe]

What does this PR do?

• Closes #9209

Remaining Work

• [x] Fix initial form state for CreateModModal if the new, unsaved mod has not been selected, which means there's no mod metadata form state anywhere -- Create modal should generate a default metadata form state in this case so that the modal doesn't appear with a bunch of field validation errors:

Product/Design micro-decisions

cc @Pashaminkovsky

• When a starter brick is picked from the menu and a new, "unsaved" mod is created, it will default to the name/label "New Mod," with a number added, counting up from 1, to avoid duplicates. So, e.g. "New Mod," "New Mod 1," "New Mod 2," etc.
• A mod component cannot be deleted or moved to another mod if it is the only component in the mod

For more information on our expectations for the PR process, see the code review principles doc

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 48.68421% with 117 lines in your changes missing coverage. Please review.

Project coverage is 74.68%. Comparing base (8318d74) to head (a56a6d8). Report is 327 commits behind head on main.

Files with missing lines	Patch %	Lines
src/pageEditor/hooks/useCreateModFromUnsavedMod.ts	29.16%	51 Missing :warning:
...geEditor/modListingPanel/modals/CreateModModal.tsx	8.82%	31 Missing :warning:
src/pageEditor/hooks/useAddNewModComponent.ts	19.04%	17 Missing :warning:
src/pageEditor/hooks/useSaveMod.ts	82.14%	10 Missing :warning:
src/pageEditor/store/editor/editorSelectors.ts	55.55%	4 Missing :warning:
.../pageEditor/tabs/modMetadata/ModMetadataEditor.tsx	62.50%	3 Missing :warning:
src/pageEditor/modListingPanel/ModComponents.tsx	0.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #9219 +/- ## ========================================== + Coverage 74.24% 74.68% +0.43% ========================================== Files 1332 1367 +35 Lines 40817 42262 +1445 Branches 7634 7895 +261 ========================================== + Hits 30306 31563 +1257 - Misses 10511 10699 +188 ```

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[github-actions[bot]]

Playwright test results

 2 failed
 123 passed
 9 flaky
 4 skipped

Details

 Open report ↗︎
 138 tests across 45 suites
 12 minutes, 48 seconds
 02ee1c5
 For more information on how to debug and view this report, see our readme

Failed tests

chrome › tests/pageEditor/brickConfiguration.spec.ts › brick configuration msedge › tests/pageEditor/brickConfiguration.spec.ts › brick configuration

Flaky tests

chrome › tests/pageEditor/addStarterBrick.spec.ts › Add starter brick to mod msedge › tests/pageEditor/addStarterBrick.spec.ts › Add starter brick to mod chrome › tests/regressions/welcomeStarterBricks.spec.ts › #8740: can view the starter mods on the pixiebrix.com/welcome page msedge › tests/regressions/welcomeStarterBricks.spec.ts › #8740: can view the starter mods on the pixiebrix.com/welcome page msedge › tests/runtime/insertAtCursor.spec.ts › Insert at Cursor › 8154: can insert at cursor after opening sidebar from selection menu chrome › tests/runtime/localIntegrations.spec.ts › Local Integrations Page › can create a new integration chrome › tests/smoke/modsPage.spec.ts › extension console mods page smoke test › can view available mods msedge › tests/smoke/sidebar.spec.ts › sidebar page smoke test › can open the sidebar from selection menu action and view the related mod's sidebar panel chrome › tests/workshop/createMod.spec.ts › can create a new mod from a yaml definition and update it

Skipped tests

chrome › tests/regressions/doNotCloseSidebarOnPageEditorSave.spec.ts › #8104: Do not automatically close the sidebar when saving in the Page Editor msedge › tests/regressions/doNotCloseSidebarOnPageEditorSave.spec.ts › #8104: Do not automatically close the sidebar when saving in the Page Editor chrome › tests/runtime/googleSheetsIntegration.spec.ts › can activate a google spreadsheet mod with config options msedge › tests/runtime/googleSheetsIntegration.spec.ts › can activate a google spreadsheet mod with config options