Add support for default arguments in C++ function templates

[maddyadams]

Description

Swift supports omitting default arguments when calling C++ functions in most circumstances, but not when the function being called is a function template

Reproduction

template <typename T>
void foo(T t, double x = 0) {}

foo(3 as CInt) // Error: Missing argument for parameter #2 in call

Expected behavior

I expected the code would compile

Environment

swift-driver version: 1.120.5 Apple Swift version 6.1 (swiftlang-6.1.0.110.21 clang-1700.0.13.3)
Target: arm64-apple-macosx15.0

Additional information

rdar://136703069