Migrate to @playcanvas/eslint-config v3 (/typescript)

[kpal81xd]

Migrates this repo to @playcanvas/eslint-config v3, adopting the /typescript subpath tier. Part of the rollout in playcanvas/eslint-config#48.

Changes

• Subpath migration: import playcanvasConfig from '@playcanvas/eslint-config' → import typescriptConfig from '@playcanvas/eslint-config/typescript'. The /typescript tier provides the typescript-eslint parser + plugin (for **/*.{js,mjs,ts}, globals.node) and the import-x resolver out of the box.
• Removed redundant wiring: dropped the manual @typescript-eslint/parser + @typescript-eslint/eslint-plugin imports and their parser/plugin config blocks, the manual import/resolver node-settings block (now supplied by the tier), and the now-defunct jsdoc/* rule overrides (the /typescript tier has no jsdoc plugin).
• Namespace: renamed import/no-unresolved → import-x/no-unresolved (v3 registers eslint-plugin-import-x natively).
• Kept the repo-specific **/*.ts extra globals (browser + mocha + node), no-use-before-define: off, and the test-file no-unused-expressions: off block.
• Dependency bump: pinned @playcanvas/eslint-config to 3.0.0-beta.5 (carries the import-x resolver fix) and removed @typescript-eslint/eslint-plugin + @typescript-eslint/parser from devDependencies (only referenced by the old config; the tier now provides them). Regenerated package-lock.json.

Auto-fixed (lint:fix)

3 source files auto-fixed (src/history.ts, src/observer-history.ts, src/observer.ts): import-x/consistent-type-specifier-style (value→type imports), redundant default-value type annotations, and stale eslint-disable directives.

Residual errors — EXPECTED, needs a separate typing pass

This is a TS lib that leans heavily on any. 154 residual errors remain after auto-fix (no config-load errors). These are intentionally NOT hand-fixed here:

rule	count	sample
@typescript-eslint/no-explicit-any	93	src/event-handle.ts:51
no-prototype-builtins	19	src/observer.ts:370
@typescript-eslint/no-this-alias	14	src/observer.ts:301
@typescript-eslint/no-unused-expressions	14	test/observer.test.mjs:35
prefer-rest-params	8	src/event-handle.ts:56
@typescript-eslint/prefer-for-of	3	src/events.ts:167
@typescript-eslint/no-unsafe-function-type	3	src/observer.ts:57
total	154

Note: the 14 @typescript-eslint/no-unused-expressions hits are chai assertions in test/observer.test.mjs. The existing test override disables the base no-unused-expressions, but the /typescript tier reports the TS-namespaced variant, which the override doesn't cover. Folded into the separate triage along with the no-explicit-any typing work.

Opened as draft because residual errors are expected and require a follow-up typing pass.