Fix use of invalid HALF_FLOAT enum

Fix use of invalid HALF_FLOAT enum

GLES 2.0 supports GL_HALF_FLOAT_OES via the OES_texture_half_float
extension. When the enum GL_HALF_FLOAT was added in GLES 3.0,
unfortunately it did not use the same enum value as GL_HALF_FLOAT_OES.
Technically, GL_HALF_FLOAT is not supported on a GLES 2.0 implementation
even with OES_texture_half_float. Fix GLES 2.0 tests to always use
GL_HALF_FLOAT_OES to avoid the issue.

Affects:

KHR-GLES2.core.internalformat.texture2d.*_half_float_*
KHR-GLES3*.core.internalformat.texture2d.*_half_float_*

Components: OpenGL

VK-GL-CTS issue: 1923

Change-Id: I9b43091382341798a0d62b9a4ec09153e915dc5c
(cherry picked from commit f7ede20a9805615a3c371b786fa7407708cf612c)