feat(operators): improve publicly exposed types

[markwhitfeld]

## PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/ngxs/store/blob/master/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[ ] Bugfix
[x] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ ] Other... Please describe:

What is the current behavior?

Issue Number: #1715

What is the new behavior?

• Expose the necessary State Operator types for the consumer of the API to more easily
  construct their own State Operators.
• Hide the AsReadOnly type so that the typescript error messaging is not referring to an internal type.
• Expose the PatchSpec type with a barred O notation so that it can be used externally, but it used with caution in case the internal type representation changes.

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

[bundlemon]

BundleMon

Files updated (1)

Status	Path	Size	Limits
✅	fesm2015/ngxs-store-operators.js	6.23KB (+13B +0.2%)	15KB / +0.5%

Unchanged files (2)

Status	Path	Size	Limits
✅	fesm2015/ngxs-store.js	88.88KB	125KB / +0.5%
✅	fesm2015/ngxs-store-internals.js	4.22KB	20KB / +0.5%

Total files change +13B +0.01%

Groups updated (1)

Status	Path	Size	Limits
✅	@ngxs/store(esm2015)[gzip] ./esm2015/**/*.js	166.82KB (+461B +0.27%)	+1%

Unchanged groups (2)

Status	Path	Size	Limits
✅	@ngxs/store(umd)[gzip] ./bundles/*.umd.js	35.32KB	+1%
✅	@ngxs/store(fesm2015)[gzip] ./fesm2015/*.js	24.02KB	+1%

Final result: ✅

View report in BundleMon website ➡️

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Current branch size history | Target branch size history

[bundlemon]

BundleMon (NGXS Plugins)

Unchanged files (14)

Status	Path	Size	Limits
✅	Plugins(umd)[gzip] storage-plugin/bundles/ngxs-storage-plugin.um d.js	7.96KB	+1%
✅	Plugins(umd)[gzip] router-plugin/bundles/ngxs-router-plugin.umd. js	7.41KB	+1%
✅	Plugins(umd)[gzip] websocket-plugin/bundles/ngxs-websocket-plugi n.umd.js	6.92KB	+1%
✅	Plugins(umd)[gzip] hmr-plugin/bundles/ngxs-hmr-plugin.umd.js	6.89KB	+1%
✅	Plugins(fesm2015)[gzip] storage-plugin/fesm2015/ngxs-storage-plugin.j s	3.64KB	+1%
✅	Plugins(umd)[gzip] form-plugin/bundles/ngxs-form-plugin.umd.js	3.41KB	+1%
✅	Plugins(fesm2015)[gzip] router-plugin/fesm2015/ngxs-router-plugin.js	3.09KB	+1%
✅	Plugins(umd)[gzip] devtools-plugin/bundles/ngxs-devtools-plugin. umd.js	2.75KB	+1%
✅	Plugins(fesm2015)[gzip] form-plugin/fesm2015/ngxs-form-plugin.js	2.65KB	+1%
✅	Plugins(fesm2015)[gzip] hmr-plugin/fesm2015/ngxs-hmr-plugin.js	2.65KB	+1%
✅	Plugins(fesm2015)[gzip] websocket-plugin/fesm2015/ngxs-websocket-plug in.js	2.59KB	+1%
✅	Plugins(umd)[gzip] logger-plugin/bundles/ngxs-logger-plugin.umd. js	2.53KB	+1%
✅	Plugins(fesm2015)[gzip] devtools-plugin/fesm2015/ngxs-devtools-plugin .js	2.17KB	+1%
✅	Plugins(fesm2015)[gzip] logger-plugin/fesm2015/ngxs-logger-plugin.js	2.01KB	+1%

No change in files bundle size

Unchanged groups (3)

Status	Path	Size	Limits
✅	All Plugins(esm2015)[gzip] ./-plugin/esm2015/**/.js	108.45KB	+1%
✅	All Plugins(umd)[gzip] ./-plugin/bundles/.umd.js	37.88KB	+1%
✅	All Plugins(fesm2015)[gzip] ./-plugin/fesm2015/.js	18.8KB	+1%

Final result: ✅

View report in BundleMon website ➡️

---

Current branch size history | Target branch size history

[bundlemon]

BundleMon (Integration Projects)

Unchanged files (3)

Status	Path	Size	Limits
✅	Main bundles(Gzip) hello-world-ng13-ivy/dist-integration/main.(h ash).js	69.83KB	+1%
✅	Main bundles(Gzip) hello-world-ng12-ivy/dist-integration/main.(h ash).js	67.99KB	+1%
✅	Main bundles(Gzip) hello-world-ng14-ivy/dist-integration/main.(h ash).js	65.5KB	+1%

No change in files bundle size

Final result: ✅

View report in BundleMon website ➡️

---

Current branch size history | Target branch size history

[codeclimate]

Code Climate has analyzed commit c592331 and detected 0 issues on this pull request.

The test coverage on the diff in this pull request is 100.0% (50% is the threshold).

This pull request will bring the total coverage in the repository to 97.0% (0.0% change).

View more on Code Climate.

[arturovt]

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