feat(ui5-search): add new property fieldLoading

[dobrinyonkov]

Description

Adds a fieldLoading property to ui5-search-field that displays a loading indicator during async search operations.

Changes

• SearchField component: Added fieldLoading boolean property (default: false)
• Collapsed mode: Shows loading state on the search button
• Expanded mode: Activates BusyIndicator wrapper around the input field
• Tests: Added Cypress tests covering both collapsed and expanded modes
• Documentation: Added "Loading State" sample demonstrating async search with 2-second delay
• Test pages: Added interactive examples to SearchField.html and Search.html

Use Case

When performing async search operations (API calls, database queries), developers can now indicate loading state to users:

searchField.addEventListener('ui5-search', async () => {
    searchField.fieldLoading = true;
    const results = await fetchSearchResults(searchField.value);
    searchField.fieldLoading = false;
});

[ui5-webcomponents-bot]

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