Visually distinguish call sites with custom calling conventions

Version and Platform (required):

• Binary Ninja Version: 3474-dev
• OS: Windows
• OS Version: 11
• CPU Architecture: x64

Bug Description:
Call sites of functions with custom calling conventions are not distinguishable from bugs. For example, opening notepad.exe gives me the following:

       140001b60  _start:
   0 @ 140001b64  __security_init_cookie()
   1 @ 140001b6d  uint64_t rbx
   2 @ 140001b6d  return sub_1400019d0(rbx) __tailcall

Does sub_1400019d0 take the register rbx via a custom calling convention, or is the entry value of rbx spilled to the stack and passed by value here? While _start makes it somewhat obvious what is going on, this can happen elsewhere.

Steps To Reproduce:
Please provide all steps required to reproduce the behavior:

1. Open any windows executable
2. Navigate to _start
3. See error

Expected Behavior:
I expect pseudo-C's semantics to match what is displayed. Specifically, imagine the use case of binja as a manual audit tool for uninitialized stack usage.

Reproduce the report by opening a Windows executable, navigating to _start, and inspecting the pseudo-C around sub_1400019d0. Trace how custom calling conventions and register arguments are displayed; done means call sites clearly distinguish a custom convention from a spilled entry register while preserving pseudo-C semantics.