[lldb] Use ReadCStringsFromMemory to speed-up AppleObjCClassDescriptorV2::method_t lookup (#172031)
With this improvement, compiling a simple Objective-C program like:
```
int main() {
@autoreleasepool {
NSDictionary *mapping = @{ @"one": @1, @"two": @2, @"three": @3 };
return 0; //breakhere
}
}
```
And running `expr -O -- mapping[@"one"]`, we can observe the following
packet count for the expression evaluation:
```
Before:
multi mem read ($MultiMemRead) : 94
read memory ($x) : 1070
After:
multi mem read ($MultiMemRead) : 188
read memory ($x) : 665
```
In other words, we save 311 packets.
Depends on:
* https://github.com/llvm/llvm-project/pull/172026
rdar://151850617
llvm-project
3cfe144f - [lldb] Use ReadCStringsFromMemory to speed-up AppleObjCClassDescriptorV2::method_t lookup (#172031)
