Fix lazy imports C API and sys.flags documentation

Replace the PyImport_SetLazyImportsMode() description, which was copied
from PyImport_ImportModuleAttrString(), and document the
sys.flags.lazy_imports attribute.

Author: brittanyrey

Doc/c-api/import.rst

@@ -366,8 +366,7 @@ Importing Modules
 
 .. c:function:: int PyImport_SetLazyImportsMode(PyImport_LazyImportsMode mode)
 
-   Similar to :c:func:`PyImport_ImportModuleAttr`, but names are UTF-8 encoded
-   strings instead of Python :class:`str` objects.
+   Sets the current lazy imports mode.
 
    This function always returns ``0``.
 

Doc/library/sys.rst

@@ -655,6 +655,11 @@ always available. Unless explicitly noted otherwise, all variables are read-only
         - :option:`-X context_aware_warnings <-X>` and
           :envvar:`PYTHON_CONTEXT_AWARE_WARNINGS`
 
+      * - .. attribute:: flags.lazy_imports
+        - :option:`-X lazy_imports <-X>` and :envvar:`PYTHON_LAZY_IMPORTS`
+          (``1`` for ``all``, ``-1`` otherwise; not changed by
+          :func:`set_lazy_imports`)
+
 
    .. versionchanged:: 3.2
       Added ``quiet`` attribute for the new :option:`-q` flag.
@@ -691,6 +696,9 @@ always available. Unless explicitly noted otherwise, all variables are read-only
    .. versionchanged:: 3.14
       Added the ``context_aware_warnings`` attribute.
 
+   .. versionchanged:: 3.15
+      Added the ``lazy_imports`` attribute.
+
 
 .. data:: float_info