Advertise EGL_ANDROID_GLES_layers extension

Presence of the extension means libEGL will scan for layers and
enumerate their entrypoints by calling AndroidGLESLayer_Initialize
and AndroidGLESLayer_GetProcAddress.

Since tools must determine layering support before fully loading
libEGL, the following call will return extension strings without
loading vendor drivers:

    eglQueryString(EGL_NO_DISPLAY, EGL_EXTENSIONS);

Bug: 110883880
Test: atest CtsGpuToolsHostTestCases
Test: Connect with GLES layers using GAPID and RenderDoc
Change-Id: Ib79193b3a0ac3dffacd51bc677b81c07ffcced93