Update `FixedArray` doc comments to match actual template param names

* The template parameter provided to `FixedArray` for the number of inline elements is named `N`
* If left defaulted, which is recommended, `FixedArray` chooses the number of inline elements by itself
* The `inline_elements` static class member contains the actual number of inlinable elements
* Previously the docs referred to the template parameter as `inline_elements` instead of `N`.

PiperOrigin-RevId: 497185546
Change-Id: I321092826d956704c0074062d2a7b924b28e36d0

absl/container/fixed_array.h

@@ -62,11 +62,10 @@ constexpr static auto kFixedArrayUseDefault = static_cast<size_t>(-1);
 // A `FixedArray` provides a run-time fixed-size array, allocating a small array
 // A `FixedArray` provides a run-time fixed-size array, allocating a small array
 // inline for efficiency.
 // inline for efficiency.
 //
 //
-// Most users should not specify an `inline_elements` argument and let
-// `FixedArray` automatically determine the number of elements
-// to store inline based on `sizeof(T)`. If `inline_elements` is specified, the
-// `FixedArray` implementation will use inline storage for arrays with a
-// length <= `inline_elements`.
+// Most users should not specify the `N` template parameter and let `FixedArray`
+// automatically determine the number of elements to store inline based on
+// `sizeof(T)`. If `N` is specified, the `FixedArray` implementation will use
+// inline storage for arrays with a length <= `N`.
 //
 //
 // Note that a `FixedArray` constructed with a `size_type` argument will
 // Note that a `FixedArray` constructed with a `size_type` argument will
 // default-initialize its values by leaving trivially constructible types
 // default-initialize its values by leaving trivially constructible types