glsl: Use | action in the lexer source to avoid duplicating the float action

glsl: Use | action in the lexer source to avoid duplicating the float action

Flex and lex have a special action ‘|’ which means to use the same action as
the next rule. We can use this to reduce a bit of code duplication in the
rules for the various float literal formats.

Reviewed-by: Matt Turner <mattst88@gmail.com>