frontend: Add switch input methods for the browser and size follow window

[a980374208]

window and enable the browser source size to adapt to changes in the browser window size

Description

This change adds input method switching support for browser sources, and implements a feature that allows the browser source page size to automatically adapt to changes of the browser interactive window size. Users can now freely adjust the browser source layout more conveniently.

Motivation and Context

Currently, the OBS browser source does not support input method switching. When text input is required, users have to use an external browser to complete input operations and copy the URL back to OBS, which brings a poor and cumbersome experience.
In addition, the browser source content cannot follow the interactive window resizing, making size adjustment inconvenient.
This PR fixes the input method switching limitation and adds responsive window adaptation for browser source, significantly improving daily usability and flexibility.

How Has This Been Tested?

Tested on Windows platform with multiple common system input methods.
Confirmed that input method switching works normally when focusing on browser source input areas.
Verified browser content scales and resizes correctly in real time when dragging or resizing the browser interactive window.
No crashes, rendering issues, performance regression or breaking changes to other existing source features.

Types of changes

• New feature (non-breaking change which adds functionality)
• Tweak (non-breaking change to improve existing functionality)

Checklist:

• I have read the contributing document.
• My code has been run through clang-format.
• My code follows the project's style guidelines
• My code is not on the master branch.
• My code has been tested.
• All commit messages are properly formatted and commits squashed where appropriate.
• I have included updates to all appropriate documentation.

[a980374208]

PR for obs-browser related changes:obsproject/obs-browser#520