chore(bridge): Refactor TS-Core bridge

Author: mjameswh

.gitignore

@@ -12,3 +12,7 @@ packages/core-bridge/releases
 packages/*/package-lock.json
 /sdk-node.iml
 *~
+
+# One test creates persisted SQLite DBs; they should normally be deleted automatically,
+# but may be left behind in some error scenarios.
+packages/test/temporal-db-*.sqlite

packages/common/src/errors.ts

@@ -20,7 +20,8 @@ export class ValueError extends Error {
 export class PayloadConverterError extends ValueError {}
 
 /**
- * Used in different parts of the SDK to note that something unexpected has happened.
+ * Signals that a requested operation can't be completed because it is illegal given the
+ * current state of the object; e.g. trying to use a resource after it has been closed.
  */
 @SymbolBasedInstanceOfError('IllegalStateError')
 export class IllegalStateError extends Error {}