[tcgc] put all scope for decorator to the last calculation priority

[tadelesh]

for the following typespec:

@clientName("Bar")
@clientName("Baz", "go")
model A {
}
 
@@clientName(A, "Foo", "csharp");
@@clientName(A, "Qux", "java");

current tcgc result for A name is:
csharp -> "Foo"
java -> "Qux"
others -> "Bar"

we received feedback about why go does not get the Baz name but get Bar.
the reason is tcgc get the @clientName decorator info for A from compiler with:
"Baz" for "go";
"Bar" for all;
"Foo" for csharp";
"Qux" for "java";
then, tcgc handle them one by one, and overwrite former with the later setting. that's our current design.

we are thinking about put the all scope to the last calculation, which could make the result more reasonable. if multiple setting for all scope, still later overwrite former, but when calculation, all scope is the last priority.

then the result for the above example should be:
csharp -> "Foo"
java -> "Qux"
go -> "Baz"
others -> "Bar"