re-do `with` conflicts: last one wins, in wasm and topdown (#3010)

* compiler/wasm: use tee_local

It's the same as set_local followed by get_local: the target variable is set
to the value from the top of the stack, but that value is retained there.

Signed-off-by: Stephan Renatus <stephan.renatus@gmail.com>

* compiler/wasm: make last 'with' statement win, update tests

Signed-off-by: Stephan Renatus <stephan.renatus@gmail.com>

* topdown/input: allow `with` overwrites that previously a conflict

This makes topdown behave more like WASM. Last `with` wins when in conflict:

    input with input.foo as "foo" with input.foo.bar as "baz"

will resolve to

    {"foo": {"bar": "baz"}}

now. Same with data references.

Signed-off-by: Stephan Renatus <stephan.renatus@gmail.com>