fix(date-range-picker): clarify two-input structure and picker toggle usage

[georgianastasov]

Closes #IgniteUI/igniteui-cli#1585

Description

Improves the Angular Date Range Picker documentation by clarifying the correct two-input setup. The update makes it clearer that inputs should be placed directly inside igx-date-range-start and igx-date-range-end, explains when igx-picker-toggle should be used, and clarifies how popup behavior differs between single-input, two-input dropdown, and dialog modes.

It also makes the examples more consistent and fixes small issues in the docs, including the disabled dates snippet and a tag typo. These changes help make the guidance easier to follow for users and reduce the chance of generating incorrect two-input date range picker markup.

Checklist:

• check topic's TOC/menu and paragraph headings
• Include TOC topic labels in topic content has a valuable update, it's new or considered as preview\ beta
• link to other topics using ../relative/path.md
• at the References section at the end of the topic add links to topics, samples, etc
• reference API documentation instead of adding a section with API

• use valid component names - [Data] Grid, IgxSelectComponent, <igx-combo>
• use spell checker tool (VS Code, Grammarly, Microsoft Editor)
• add inline code blocks for the names of classes / tags / properties
• add language descriptor for the code blocks
• check broken links (use browser add-on)
• check if sample is working and fully visible in the topic
• check if sample is working and fully visible in the StackBlitz
• check if code blocks match the code in StackBlitz demo

• follow SEO guidelines to fill topic's metadata (SEO guidelines)

• do not resolve requested changes (leave that to the reviewer)
• add pending-localization label when the review of the PR is done
• add a member from the localization team to translate it

[Copilot]

Pull request overview

Updates the Angular Date Range Picker documentation to better explain the correct two-input configuration (start/end editors), including how to wire up picker toggle/clear actions and how popup behavior differs across dropdown vs dialog modes.

Changes:

• Expanded the two-input example markup to include igx-picker-toggle/igx-picker-clear and clarified where inputs should be projected.
• Clarified calendar popup opening behavior for single-input vs two-input configurations across dropdown and dialog modes.
• Fixed minor documentation issues (disabled dates snippet, heading capitalization, and a tag typo).

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The base branch was changed.