asahi: Rewrite state emit code using information from the Mesa PowerVR driver

Looking at PowerVR's PPP definitions in tree in Mesa
(src/imagination/csbgen/), we find that AGX's "tagged" data structures
are actually sequences of state items prefixed by a header specifying
which state follows. Rather than hardcoding the sequences in which Apple's
driver chooses to bundle state, we need the XML to be flexible enough to
encode or decode any valid combination of state. That means reworking
the XML. While doing so, we find a number of fields that are identical
between RGX and AGX, and fix the names while at it (for example, the W
Clamp floating point).

Names are from the PowerVR code in Mesa where sensible.

Once we've reworked the XML, we need to rework the decoder.  Instead of
reading tags and printing the combined state packets, the decoder now
must unpack the header and print the individual state items specified by
the header, with slightly more complicated bounds checking.

Finally, state emission in the driver becomes much more flexible. To
prove the flexibility actually works, we now emit all PPP state (except for
viewport and scissor state) as a single PPP update. This works. After
this we can move onto more interesting arrangements of state for lower
driver overhead.

Now that we have fine grained state emit code, let's use it to reduce
driver overhead. Dirty tracking is delicate: while this seems to work,
I've also added an ASAHI_MESA_DEBUG=dirty option in debug builds
to disable the optimizations here for future debug.