Advertise filtering support for FP16 luminance/alpha formats on ES 3.0. Now that these formats are emulated if necessary on ES 3.0 contexts, advertise filtering support as well. This enables OES_texture_half_float_linear on mobile devices which support ES 3.0 but don't advertise this extension. Bug: angleproject:4648 Change-Id: I09f00fbb1454b2cfa72295254fbc45c872f4919c Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2210701 Reviewed-by: Jonah Ryan-Davis <jonahr@google.com> Reviewed-by: Geoff Lang <geofflang@chromium.org> Commit-Queue: Kenneth Russell <kbr@chromium.org>