Calling Surface::get_current_texture is not idempotent

[udoprog]

Relates to the question posed in: #4967
Relates to #5138

Description

When using native backends, Surface::get_current_texture currently calls directly into the backend to return a surface texture, this call is not idempotent in wgpu-core.

A handle to the same texture should instead be returned until it has "expired". Which happens through (among other things) it being presented or the underlying surface being reconfigured.

While calling Surface::get_current_texture multiple times would be atypical, the API does not prevent a user from doing so. @grovesNL noted on matrix that the specified behavior is to return the same texture until it is expired.

Platform

Vulkan: This would allow the caller to exhaust the available wait semaphores before they have been used correctly (by presenting the surface). This might cause strange synchronization issues - the exact behavior would depend on timing, the state of the semaphores, and the Vulkan implementation in question.

I have not looked into the behavior of other backends.