Getting TraceID from an OpenTracing DatadogSpanContext can throw "Cannot read properties of undefined (reading 'toString')

Calling this `DatadogSpanContext.toTraceId()` method on what appears to be a valid span can sometimes error out with an undefined inner `this._traceId` value:

https://github.com/DataDog/dd-trace-js/blob/497c0b0d4333b6a7e7a434fb4de275595e5950c9/packages/dd-trace/src/opentracing/span_context.js#L33-L40

### Suggested Solution

- While I am not sure what might cause this scenario, a quick fix would be to make the dot property access of `this._traceId` a bit more defensive:

    ```
     toTraceId (get128bitId = false) {
        if (this._traceId && get128bitId) {
          return this._traceId.toBuffer().length <= 8 && this._trace.tags[TRACE_ID_128]
            ? this._trace.tags[TRACE_ID_128] + this._traceId.toString(16).padStart(16, '0')
            : this._traceId.toString(16).padStart(32, '0')
        }
        return this._traceId?.toString(10)
      }
    ```

### Replication Steps

- Using:

    ```
        "dd-trace": "5.25.0",
    ```
- Initialize the tracer on startup:

    ```
    import tracer from 'dd-trace';
    import { version } from '../../package.json';
    import { buildVars } from '#root/.build/buildVars';
    
    tracer.init({
      service: process.env.DD_SERVICE || 'my-fe-app',
      version: version ? `${version}-${buildVars.GIT_SHA}` : '0.0.0',
      tags: {
        pid: process.pid,
      },
      runtimeMetrics: true,
      logInjection: true,
    });
    ```

- Try to defensively get the active span's `traceID` at runtime

    ```nodejs
    import tracer from 'dd-trace';
    
    ...
    
        const span = tracer.scope().active();
        const traceID = span?.context()?.toTraceId() ?? 'n/a';

    ...
    ```

### Expected result

- `traceID` is either a valid Trace ID from the current span or `undefined` in which case we default to `'n/a/` based on the code above

### Actual result

- We regularly encounter an error whereby we seem to have a defined `span` (i.e. not `null` or `undefined`) with an empty or missing `DatadogSpanContext._traceID` property such that when we call `toTraceId()` on it we get the following error:

    ```
    .../my_app/node_modules/dd-trace/packages/dd-trace/src/opentracing/span_context.js:39
         return this._traceId.toString(10)
                                          ^
    TypeError: Cannot read properties of undefined (reading 'toString')
         at DatadogSpanContext.toTraceId (.../my_app/packages/dd-trace/src/opentracing/span_context.js:39:26)
    ```

### Unit Tests

- Here is a failing test we can add to `packages/dd-trace/test/opentracing/span_context.spec.js` to demonstrate the issue
    
    ```
    'use strict'

    require('../setup/tap')

    const { expect } = require('chai')
    const id = require('../../src/id')

    describe('SpanContext', () => {
      let SpanContext
      let TraceState

      beforeEach(() => {
        SpanContext = require('../../src/opentracing/span_context')
        TraceState = require('../../src/opentracing/propagation/tracestate')
      })
     
      ...
      describe('toTraceparent()', () => {
      ...
    
        it('should allow nullsafe access to trace ID', () => {
          const spanContext = new SpanContext({
            traceId: undefined,
            spanId: id('456', 16)
          })
    
          spanContext._trace.tags['_dd.p.tid'] = null
    
          expect(spanContext.toTraceId()).to.equal(undefined)
        })
      })
    })
    ```

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Getting TraceID from an OpenTracing DatadogSpanContext can throw "Cannot read properties of undefined (reading 'toString') #4987

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	toTraceId (get128bitId = false) {
	if (get128bitId) {
	return this._traceId.toBuffer().length <= 8 && this._trace.tags[TRACE_ID_128]
	? this._trace.tags[TRACE_ID_128] + this._traceId.toString(16).padStart(16, '0')
	: this._traceId.toString(16).padStart(32, '0')
	}
	return this._traceId.toString(10)
	}