graphics/glslang: Update to 16.2.0

While here, add "shared" flavor for installing shared
libraries. (Default is static.)

Changelog: https://github.com/KhronosGroup/glslang/blob/16.2.0/CHANGES.md

PR: 292737
Reported by: Eric Camachat <eric@camachat.org>,

		vvd

Co-authored-by: Eric Camachat <eric@camachat.org>