feat(core): Export TracesSamplerSamplingContext type (#17523)

In #15277,
`TracesSamplerSamplingContext` is added to and exported from
[types-hoist], but is not being exported from [index.ts].

I'm following the [instruction], and I want to inject `(samplingContext:
TracesSamplerSamplingContext) => number | boolean` to a function that is
wrapping `Sentry.init`, but I can't because
`TracesSamplerSamplingContext` is not recognized :(

<!--link-->
[types-hoist]:
https://github.com/getsentry/sentry-javascript/blob/14eba5676149317f2e2b31143a0590256d32c094/packages/core/src/types-hoist/samplingcontext.ts#L47
[index.ts]:
https://github.com/getsentry/sentry-javascript/blob/14eba5676149317f2e2b31143a0590256d32c094/packages/core/src/index.ts#L403
[instruction]:
https://docs.sentry.io/platforms/javascript/guides/react/tracing/configure-sampling/#sampling-function-tracessampler

Author: dolbin-prime

packages/core/src/index.ts

@@ -410,7 +410,11 @@ export type { Stacktrace, StackParser, StackLineParser, StackLineParserFn } from
 export type { PropagationContext, TracePropagationTargets, SerializedTraceData } from './types-hoist/tracing';
 export type { StartSpanOptions } from './types-hoist/startSpanOptions';
 export type { TraceparentData, TransactionSource } from './types-hoist/transaction';
-export type { CustomSamplingContext, SamplingContext } from './types-hoist/samplingcontext';
+export type {
+  TracesSamplerSamplingContext,
+  CustomSamplingContext,
+  SamplingContext,
+} from './types-hoist/samplingcontext';
 export type {
   DurationUnit,
   InformationUnit,