Drop TracerClock from start/withSpan APIs, but use internally

[fabianfett]

public protocol TracerProtocol: LegacyTracerProtocol {
    /// The concrete type of span this tracer will be producing/
    associatedtype Span: Tracing.Span

    /// Start a new ``Span`` with the given `Baggage`.
    ///
    /// The current task-local `Baggage` is picked up and provided to the underlying tracer.
    /// It is also possible to pass a specific `baggage` explicitly, in which case attempting
    /// to pick up the task-local baggage is prevented. This can be useful when we know that
    /// we're about to start a top-level span, or if a span should be started from a different,
    /// stored away previously,
    ///
    /// - Note: Prefer ``withSpan(_:baggage:ofKind:at:function:file:line:operation:)`` to start
    ///   a span as it automatically takes care of ending the span, and recording errors when thrown.
    ///   Use `startSpan` iff you need to pass the span manually to a different
    ///   location in your source code to end it.
    ///
    /// - Warning: You must `end()` the span when it the measured operation has completed explicitly,
    ///   otherwise the span object will potentially never be released nor reported.
    ///
    /// - Parameters:
    ///   - operationName: The name of the operation being traced. This may be a handler function, database call, ...
    ///   - baggage: The `Baggage` providing information on where to start the new ``Span``.
    ///   - kind: The ``SpanKind`` of the new ``Span``.
    ///   - clock: The clock to use as time source for the start time of the ``Span``
    ///   - function: The function name in which the span was started
    ///   - fileID: The `fileID` where the span was started.
    ///   - line: The file line where the span was started.
    func startSpan(
        _ operationName: String,
        baggage: @autoclosure () -> Baggage,
        ofKind kind: SpanKind,
        clock: some TracerInstantProtocol,
        function: String,
        file fileID: String,
        line: UInt
    ) -> TracerSpan

    func startSpan(
        _ operationName: String,
        baggage: @autoclosure () -> Baggage,
        ofKind kind: SpanKind,
        function: String,
        file fileID: String,
        line: UInt
    ) -> TracerSpan
}

extension TracerProtocol {
    func startSpan(
        _ operationName: String,
        baggage: @autoclosure () -> Baggage,
        ofKind kind: SpanKind,
        function: String,
        file fileID: String,
        line: UInt
    ) -> TracerSpan {

    }
}