[lldb][swig] Support SBFileSpec::GetPath (#162964)
# Summary
`SBFileSpec::GetPath(char *dst_path, size_t dst_len)` contains `char*`
type argument. Need to handle this for python. Fortunately there're
already similar definitions we can reuse.
# Test Plan
Start the freshly built lldb and run the following code
```
$ lldb
(lldb) script
Python Interactive Interpreter. To exit, type 'quit()', 'exit()' or Ctrl-D.
>>> debugger = lldb.SBDebugger.Create()
>>> debugger.SetAsync (False)
>>> target = debugger.CreateTarget("~/tmp/hello")
>>> target.IsValid()
True
>>> breakpoint = target.BreakpointCreateByName('main', 'hello')
>>> breakpoint.GetNumLocations()
1
>>> process = target.LaunchSimple (None, None, os.getcwd())
>>> process.IsValid()
True
>>> thread = process.GetThreadAtIndex(0)
>>> frame = thread.GetFrameAtIndex(0)
>>> line = frame.GetLineEntry()
# Important line below
>>> file = line.GetFileSpec().GetPath(1024)
# Important line above
>>> print(file)
/home/wanyi/tmp/main.cpp
```
## Before this change
```
$ lldb
(lldb) script
Python Interactive Interpreter. To exit, type 'quit()', 'exit()' or Ctrl-D.
>>> debugger = lldb.SBDebugger.Create()
>>> debugger.SetAsync (False)
>>> target = debugger.CreateTarget("~/tmp/hello")
>>> target.IsValid()
True
>>> breakpoint = target.BreakpointCreateByName('main', 'hello')
>>> breakpoint.GetNumLocations()
1
>>> process = target.LaunchSimple (None, None, os.getcwd())
>>> process.IsValid()
True
>>> thread = process.GetThreadAtIndex(0)
>>> frame = thread.GetFrameAtIndex(0)
>>> line = frame.GetLineEntry()
>>> file = line.GetFileSpec().GetPath(1024)
Traceback (most recent call last):
File "<console>", line 1, in <module>
TypeError: SBFileSpec.GetPath() missing 1 required positional argument: 'dst_len'
>>> print(file)
Traceback (most recent call last):
File "<console>", line 1, in <module>
NameError: name 'file' is not defined
```
