vkEnumerateInstanceExtensionProperties is incorrectly implemented

**Environment:**
- OS: Windows
- GPU and driver version: NVIDIA GEFORCE RTX 3090
- SDK or header version if building from repo: 1.3.280.0
- Options enabled (synchronization, best practices, etc.):

**Describe the Issue**
vkEnumerateInstanceExtensionProperties is a "pre-instance function" (https://vulkan.lunarg.com/doc/view/1.3.280.0/windows/loader_and_layer_interface.html#user-content-pre-instance-functions), and therefore requires special handling via `Vk...Chain` in order to be properly layered. Because this is not properly implemented, VVL's `EnumerateInstanceExtensionProperties()` function does not appear to ever get executed.

For example, calling: `vkEnumerateInstanceExtensionProperties(NULL, NULL, NULL)` will not report the `VUID-vkEnumerateInstanceExtensionProperties-pPropertyCount-parameter` validation error.

It's also worth noting that if an app calls `vkEnumerateInstanceExtensionProperties()` prior to `vkCreateInstance()`, the `VkLayer_khronos_validation.dll` does not get loaded, as would be expected if the function was correctly layered.

Lastly, the `chassis.cpp::EnumerateInstanceExtensionProperties()` implementation does not correctly handle the case when `pLayerName == NULL`

This set of issues likely applies to the other "pre-instance functions".

**Expected behavior**
1. Calls to `vkEnumerateInstanceExtensionProperties()` prior to `vkCreateInstance()` would load `VkLayer_khronos_validation.dll` and run validation checks
2. Calling `vkEnumerateInstanceExtensionProperties(NULL, NULL, NULL)` should report `VUID-vkEnumerateInstanceExtensionProperties-pPropertyCount-parameter` validation error.
3. Calling `vkEnumerateInstanceExtensionProperties(NULL, &count, NULL)` should result in VVL calling down the chain so that `extensions provided by the Vulkan implementation or by implicitly enabled layers are returned` (per vkEnumerateInstanceExtensionProperties's spec)

**Valid Usage ID**
VUID-vkEnumerateInstanceExtensionProperties-* don't get reported

**Additional context**
It's worth noting that according to the vulkan spec, VVL is not actually allowed layer the pre-instance functions: `In order to intercept the pre-instance functions, several conditions must be met: ... The layer must be implicit`. I'm not sure how VVL is expected to reconcile that, but thought it would be worth mentioning.

Start by tracing pre-instance function dispatch and layering for vkEnumerateInstanceExtensionProperties before vkCreateInstance(), then inspect chassis.cpp::EnumerateInstanceExtensionProperties(). Reproduce the calls with NULL parameters and verify validation reporting, layer loading, and extension results against the expected behavior and VUID.

Written by the indexing model from the issue text.