[FIX] Refresh texture state when toggling mipmaps

[willeastcott]

Fixes playcanvas/editor#1187

Summary

• update Texture#mipmaps to recalculate mip level count when toggled at runtime
• mark minification filter parameters dirty when mipmaps changes so sampler state updates immediately
• preserve existing mip upload scheduling when enabling mipmaps and keep current WebGPU/integer-format guards
• addresses the viewport update behavior reported in Changing the Mipmaps checkbox does not update the game scene images editor#1187

Test plan

• linked Editor to this Engine branch and confirmed toggling texture Mipmaps updates viewport visuals immediately
• confirmed no filtering-mode change or scene reload is needed after toggling mipmaps
• confirmed PR scope is only src/platform/graphics/texture.js
• no new automated test file included in this PR (by request)

[Copilot]

Pull request overview

Updates PlayCanvas Engine texture runtime behavior so toggling Texture#mipmaps recalculates mip level count and forces sampler minification state to refresh immediately, addressing Editor viewport update issues when mipmaps are toggled at runtime.

Changes:

• Recalculate Texture._numLevels when mipmaps is toggled at runtime (_updateNumLevel()).
• Mark minification filter state dirty when mipmaps changes to refresh sampler state immediately.
• Preserve existing mipmap upload scheduling when enabling mipmaps, with existing WebGPU / integer-format guards.

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