refactor: function! macro for error context (#317)

Deletes any now-superfluous `const NAME: &'static str = "name";` definitions.

This gives a path to the function that is being called, which is useful
for debugging errors. It replaces the necessity of implementing
`const NAME: &'static str = "name";` in every function that wants to
use these macros (or coming up with a custom context).

crates/ironrdp-testsuite-core/tests/pcb.rs

@@ -129,7 +129,7 @@ fn truncated() {
 
     expect![[r#"
             Error {
-                context: "PreconnectionBlob",
+                context: "<ironrdp_pdu::pcb::PreconnectionBlob as ironrdp_pdu::PduDecode>::decode",
                 kind: NotEnoughBytes {
                     received: 0,
                     expected: 239,