Add telemetry support for loading external tokens and related events

[konstantin-msft]

This pull request introduces telemetry support for loading external tokens and related events in the MSAL browser and common packages. The main focus is on instrumenting the TokenCache flow to provide detailed performance measurements for the loading of external tokens and its internal operations. Comprehensive tests have been added to ensure correct telemetry instrumentation and error handling.

Telemetry instrumentation for external token loading

• Added new performance event types for external token loading and its sub-operations (LoadExternalTokens, LoadAccount, LoadIdToken, LoadAccessToken, LoadRefreshToken) in PerformanceEvent.ts.
• Refactored TokenCache to accept a performanceClient and instrument the loadExternalTokens method and its internal functions using performance measurements, including error handling. [1] [2] [3] [4] [5] [6] [7]

Test coverage for telemetry

• Expanded TokenCache.spec.ts tests to verify top-level and sub-operation telemetry events, including success and error scenarios for loadExternalTokens. [1] [2]

Package change logs

• Updated change logs for both @azure/msal-browser and @azure/msal-common to reflect the addition of telemetry support for loading external tokens and related events. [1] [2]

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