fix(sqllab): invalid empty state on switch tab

[justinpark]

SUMMARY

The current DB selection empty state screen is modified through the setEmptyState function. As a result, when tabs switch and share the same DB selection ID, the setEmptyState call is ignored, leading to a bug where the empty state is displayed even when a DB is selected.

This commit unifies the state management by using useMemo to ensure that the showEmpty value is always set when there is a currently selected DB.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

Before:

before--empty-on-switch-tab.mov

After:

after--empty-on-switch-tab.mov

TESTING INSTRUCTIONS

Open multiple tabs that selects the same db and then switch tabs each others

ADDITIONAL INFORMATION

• Has associated issue:
• Required feature flags:
• Changes UI
• Includes DB Migration (follow approval process in SIP-59)
  • Migration is atomic, supports rollback & is backwards-compatible
  • Confirm DB migration upgrade and downgrade tested
  • Runtime estimates and downtime expectations provided
• Introduces new feature or API
• Removes existing feature or API