nir/algebraic: Flag inexact optimizations
nir/algebraic: Flag inexact optimizations

Many of our optimizations, while great for cutting shaders down to size,
aren't really precision-safe.  This commit tries to flag all of the
inexact floating-point optimizations so they don't get run on values that
are flagged "exact".  It's a bit conservative and maybe flags some safe
optimizations as unsafe but that's better than missing one.

Reviewed-by: Francisco Jerez <5906ff32bdd9fd8db196f6ba5ad3afd6f9257ea5@riseup.net>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler