* Add tracing support to tsserver
Read the `TSS_TRACE` environment variable to determine which directory
trace files should be written to.
Notable changes from tsc tracing:
1) Drop all tracepoints that depend on type IDs
2) Write output to trace.PID.json
3) New, server-specific events (request/response, cancellation, etc)
* Drop try-finally blocks that aren't strictly necessary
* Fix lint error
* Trace background work (for diagnostics)
* Move try-finally blocks into session so tsc doesn't use them
* Add missing try-finally
* Use consistent capitalization
* Inline canPop call where underlying variable is available
* Clarify comments
* Include PID in build-mode file names
* Introduce more efficient popAll function
* Trace throwIfCancellationRequested rather than isCancellationRequested
* Remove unnecessary try-finally blocks
* Add a command-line argument for consistency with logging
* Fix rebase issues
* Address PR feedback
* Rename completionEvents to eventStack
* Drop assertStackEmpty as hard-to-maintain and marginally valuable
* Rename stepCancellation to stepCanceledEarly
* Rename stepEarlyCancellation to stepCanceled and use flag instead
* Check correct variable on exit
* Add full implemention of Map and Set to shims
* Update default Map interface
* Remove WeakMap/WeakSet
* Add tests for set shim
* Update most usages of Map<K, true> to Set
* PR Feedback
* Fix lint issues
* Change key in fsWatchCallback
* Simpler shim, more tests
* Fix typo in collection shim
* Increase selectivity of subtype relationship for signatures
* Add regression test
* Accept new baselines
* Use strictSubtypeRelation for union subtype reduction
* (x: number | undefined) -> void is subtype of (x?: number | undefined) => void
* Accept new baselines
* Add tests
* Accept new baselines
* Address CR feedback
* Fix parameter list length check
* Accept API baseline changes
* Create different watch options in compiler options
* Thread through the new watch options
* Actually use the options passed through for watch strategy
* Support delay on updating child directory watches
* Make watchOptions separate from compilerOptions
* Support passing watch options from command line
* Handle displaying of watchOptions
