Fix metadata availability testing for parameterized existentials and implement it for @isolated(any) function types

[rjmccall]

The existing testing was pretty broken: we were diagnosing all sorts of things that don't require type metadata (like using a tuple with an extended existential in a value position in an API signature) and not diagnosing several things that do (like covariant function conversions that erase types). There's therefore some risk to this patch, but I'm not too worried because needing metadata like this is pretty uncommon, and it's likely that programs won't build correctly anyway --- it'll just get caught by the linker instead of the compiler.

[rjmccall]

@swift-ci Please test

[rjmccall]

@swift-ci Please test

[rjmccall]

@swift-ci Please test

[rjmccall]

@swift-ci Please test

[kateinoigakukun]

It seems like the first flag argument of swift_getExtendedFunctionTypeMetadata is somehow represented as i64 on 32-bit arch 🤔 As far as I checked, the argument is constructed as SizeTy, so I'm not sure what makes it to be i64.

https://ci.swift.org/job/oss-swift-pr-test-crosscompile-wasm-ubuntu-20_04/66/

/home/build-user/swift/test/IRGen/isolated_any_metadata.sil:24:20: error: CHECK-ACCESSOR: expected string not found in input
// CHECK-ACCESSOR: call ptr @swift_getExtendedFunctionTypeMetadata([[INT]] 2214592512, [[INT]] 0, ptr null, ptr null, ptr getelementptr inbounds {{.*}} @"$sytN"{{.*}}), ptr null, i32 2, ptr null)
                   ^
<stdin>:28:73: note: scanning from here
define linkonce_odr hidden swiftcc %swift.metadata_response @"$syyYAcMa"(i64 %0) #1 {
                                                                        ^
<stdin>:28:73: note: with "INT" equal to "i32"
define linkonce_odr hidden swiftcc %swift.metadata_response @"$syyYAcMa"(i64 %0) #1 {
                                                                        ^
<stdin>:28:73: note: with "INT" equal to "i32"
define linkonce_odr hidden swiftcc %swift.metadata_response @"$syyYAcMa"(i64 %0) #1 {
                                                                        ^
<stdin>:35:5: note: possible intended match here
 %3 = call ptr @swift_getExtendedFunctionTypeMetadata(i64 2214592512, i64 0, ptr null, ptr null, ptr getelementptr inbounds (%swift.full_existential_type, ptr @"$sytN", i32 0, i32 1), ptr null, i32 2, ptr null) #2
    ^