reflect: implement MakeChan

[0pcom]

reflect.MakeChan currently panics with "unimplemented". This implements it.

It completes a small gap: MakeSlice, MakeMap and New are all supported, so code that builds a channel reflectively is the odd one out — and it is reached by generic container and codec libraries that construct channel types from a reflect.Type.

Verified by building TinyGo and running the compiler test suite.

[dgryski]

Please add a test for this new function. For reflect, this can either be in testdata/reflect.go or reflect/value_test.go.

[0pcom]

Added TestTinyMakeChan in src/reflect/value_test.go, and rebased on dev.

It covers buffered and unbuffered creation (kind, Cap, Len, and a real send/receive through Interface(), since Value.Send/Value.Recv are still unimplemented), plus the three panic paths: non-channel type, negative buffer size, and a unidirectional channel type.

On verification: CI has not run on this PR, so I checked the test's expectations against the host reflect package, where it passes — that pins the behaviour to upstream semantics. I could not run it against these sources under a released TinyGo binary (the musl build gets in the way), so the implementation itself is still only verified by reading.