[wpe-2.38] after WEBGL_lose_context cycle context gets detached from the page

[BunioFH]

test: https://bunsoft.dev/webgl3d.html?dropgl=true uses WEBGL_lose_context extension to simulate context being lost and attempts to obtain it once again during resume/suspend cycle. on freeze event context is lost using loseContext which produces webglcontextlost event, in it's handling restoreContext is attempted and exactly as it is defined in the test it works but the screen itself even though logs show differently remains blank.

note that failure handling on vertex shader compilation is not required on a google chrome and to my taste should not be on any browser. test should produce failure in gl.clear and attempt to restore context after that.

issue related to change from #1538