[LoongArch] Implement LoongArchRegisterInfo::canRealignStack() (#76913)

This patch fixes the crash issue in the test:
CodeGen/LoongArch/can-not-realign-stack.ll

Register allocator may spill virtual registers to the stack, which    
introduces stack alignment requirements (when the size of spilled     
    registers exceeds the default alignment size of the stack). If a  
function does not have stack alignment requirements before register   
allocation, registers used for stack alignment will not be preserved. 

Therefore, we should implement `canRealignStack()` to inform the      
register allocator whether it is allowed to perform stack realignment 
operations.