[clang-tools-extra] [clang-tidy] Add options to throw unannotated functions in `bugprone-exception-escape` (PR #168324)

[Baranov Victor via cfe-commits]

================
@@ -71,3 +71,22 @@ Options
 
    Comma separated list containing type names which are not counted as thrown
    exceptions in the check. Default value is an empty string.
+
+.. option:: TreatFunctionsWithoutSpecificationAsThrowing
+
+   Determines which functions are considered as throwing if they do not have
+   an explicit exception specification. It can be set to the following values:
+
+   - `None`
+      The check will consider functions without an explicit exception
+      specification as throwing only if they have a visible definition which
+      can be deduced to throw.
+   - `OnlyUndefined`
+      The check will consider functions with only a declaration available as
+      throwing.
----------------
vbvictor wrote:

```suggestion
      The check will consider functions with only a declaration available and
      no visible definition as throwing.
```
Since we use term `definition` in other descriptions, lets follow the same pattern here.

https://github.com/llvm/llvm-project/pull/168324