Make position translation to UTF16 more robust #1057

Job	Run time
static analysis (Elixir 1.15.x \| Erlang/OTP 25.x)	19s
mix test windows (Elixir 1.13.x \| Erlang/OTP 22.x)	7m 28s
mix test (Elixir 1.13.x \| Erlang/OTP 22.x)	5m 21s
mix test windows (Elixir 1.13.x \| Erlang/OTP 23.x)	9m 56s
mix test (Elixir 1.13.x \| Erlang/OTP 23.x)	6m 15s
mix test windows (Elixir 1.13.x \| Erlang/OTP 24.x)	6m 12s
mix test (Elixir 1.13.x \| Erlang/OTP 24.x)	4m 32s
mix test windows (Elixir 1.13.x \| Erlang/OTP 25.x)	5m 30s
mix test (Elixir 1.13.x \| Erlang/OTP 25.x)	4m 1s
mix test windows (Elixir 1.14.x \| Erlang/OTP 23.x)	8m 49s
mix test (Elixir 1.14.x \| Erlang/OTP 23.x)	7m 15s
mix test windows (Elixir 1.14.x \| Erlang/OTP 24.x)	6m 38s
mix test (Elixir 1.14.x \| Erlang/OTP 24.x)	4m 45s
mix test windows (Elixir 1.14.x \| Erlang/OTP 25.x)	5m 42s
mix test (Elixir 1.14.x \| Erlang/OTP 25.x)	5m 8s
mix test windows (Elixir 1.15.x \| Erlang/OTP 24.x)	6m 42s
mix test windows (Elixir 1.15.x \| Erlang/OTP 25.x)	5m 30s
mix test (Elixir 1.15.x \| Erlang/OTP 24.x)	4m 28s
mix test (Elixir 1.15.x \| Erlang/OTP 25.x)	5m 23s
	1h 49m 54s

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