[clang] [docs] Add a more detailed description in CXString.h. (PR #119090)

[via cfe-commits]

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@@ -46,6 +46,9 @@ typedef struct {
 
 /**
  * Retrieve the character data associated with the given string.
+ *
+ * The caller shouldn't free the returned string data, and the returned string
+ * data shouldn't be accessed after the \c CXString disposed.
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iseki0 wrote:

> The validity here is referring to lifetimes in C/C++, which is normally described as \"valid\".

Great, but the string data is not valid during the whole lifetime of CXString. In opposite, it's only valid before we call the `clang_disposeString`.

https://github.com/llvm/llvm-project/pull/119090