Autogenerate (de)serialization for Extended Instruction Sets

A generic mechanism for (de)serialization of extended instruction sets
is added with this CL. To facilitate this, a new class
"SPV_ExtendedInstSetOp" is added which is a base class for all
operations corresponding to extended instruction sets. The methods to
(de)serialization such ops as well as its dispatch is generated
automatically.

The behavior controlled by autogenSerialization and hasOpcode is also
slightly modified to enable this. They are now decoupled.
1) Setting hasOpcode=1 means the operation has a corresponding
   opcode in SPIR-V binary format, and its dispatch for
   (de)serialization is automatically generated.
2) Setting autogenSerialization=1 generates the function for
   (de)serialization automatically.
So now it is possible to have hasOpcode=0 and autogenSerialization=1
(for example SPV_ExtendedInstSetOp).

Since the dispatch functions is also auto-generated, the input file
needs to contain all operations. To this effect, SPIRVGLSLOps.td is
included into SPIRVOps.td. This makes the previously added
SPIRVGLSLOps.h and SPIRVGLSLOps.cpp unnecessary, and are deleted.

The SPIRVUtilsGen.cpp is also changed to make better use of
formatv,making the code more readable.

PiperOrigin-RevId: 269456263