feat(ui5-toolbar-item): add shrink-content property

[NakataCode]

Problem

When a ui5-toolbar-item with overflow-priority="NeverOverflow" contains wide content (e.g. a ui5-title with long text), it pushes other items — including the overflow button — completely out of view. This is because all toolbar item wrappers have flex-shrink: 0, so nothing yields space.

The spec clarifies that the toolbar has no built-in mechanism for long content in small viewports, and NeverOverflow only guarantees the item won't go to the popover — it makes no promise about layout when the item exceeds the container width. Titles are also intended to be short control-group labels per the Fiori spec, so automatic shrinking behavior would be surprising and could break existing layouts.

Solution

Add an opt-in shrink-content boolean property to ui5-toolbar-item. When set, the item's wrapper receives the existing .ui5-tb-self-overflow CSS class (flex-shrink: 1; flex-grow: 1; min-width: 2.5rem), allowing it to yield space to other items instead of pushing them out.

Implementation details

• shrinkContent property on ToolbarItem — opt-in, default false
• hasOverflow getter returns true when shrinkContent is set, hooking into the existing self-overflow CSS path with no new CSS required
• clampMaxWidth getter added to ToolbarItemBase (returns true by default, following the existing behavioral flag pattern of hasOverflow, isSeparator, ignoreSpace etc.). Overridden in ToolbarItem to return !this.shrinkContent, preventing the max-width capping logic in addItemsAdditionalProperties from permanently freezing the item at its first-render width
• shrinkContent items excluded from minWidth accumulation in storeItemsWidth — their rendered width is flex-distributed, not a stable natural width

Usage

<ui5-toolbar align-content="Start">
    <ui5-toolbar-item overflow-priority="NeverOverflow" shrink-content>
        <ui5-title wrapping-type="None">Long title that should yield space...</ui5-title>
    </ui5-toolbar-item>
    <ui5-toolbar-button text="Edit"></ui5-toolbar-button>
</ui5-toolbar>

Fixes #13768

[sap-ui5-webcomponents-release]

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