perf(shader): reserve an IR value's arguments for its opcode at creation

Every IR value grew its argument vector one AddArgument at a time from
empty, so a value with three arguments allocated three times (capacity
1, 2 and then 4) and freed the first two. The constructor now reserves
IrOpcodeOperandCount(opcode) arguments, the count IrBuilder::Emit
already requires, so a value built with its opcode's arguments
allocates once. Opcodes without fixed arguments (constants, phis)
reserve nothing, as before. The IR and the SPIR-V are unchanged.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

core/shader/recompiler/IntermediateRepresentation/src/IrValue.cpp

@@ -6,6 +6,7 @@
 namespace ShaderRecompiler {
 
 IrValue::IrValue(IrOpcode opcode, IrType type, std::uint32_t id) : opcode(opcode), type(type), id(id), hasImmediate(false), parent(nullptr) {
+    arguments.reserve(IrOpcodeOperandCount(opcode));
 }
 
 std::uint32_t IrValue::Id() const {