Doclink: Support linking interfaces

[yuandrew]

What was changed

Added fix for doclink linking interfaces

Why?

We want these linked

Checklist

1. Closes Doclink: interfaces are not linked #2213

2. How was this tested:

3. Any docs updates needed?

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Note

Low Risk
Changes are limited to the doclink dev tool, generated doc comments, and test synchronization; no runtime SDK behavior changes.

Overview
Fixes the doclink tool so -fix can add // Exposed as: [go.temporal.io/sdk/...] comments for types declared inside grouped type (...) blocks—especially interfaces and simple named types like SessionState int—which were previously skipped because matching only looked at the third token (type Foo Bar).

Matching now strips trailing // comments before parsing and treats grouped type lines where the name is the first token (e.g. ContextPropagator interface {). Bare embedded interface fields (e.g. SendChannel inside Channel interface) are no longer mistaken for type definitions. Internal file walks re-open files for the doc check pass and close handles with returned errors instead of defer + log.Fatal.

Adds unit/integration-style tests for the matcher and processInternal. Running the tool updates many internal symbols (workflow channels/selectors, headers, schedules, deployments, temporal errors, etc.) with missing exposure links. Shutdown tests use buffered pollStarted channels to avoid races.

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