fix: discriminator-based resolution

[kol-93]

Description

Fixed:

• type discriminator property deleted from source object after plainToInstance/instanceToPlain
• cannot read property name of undefined/cannot read property constructor of null when trying to transform non-object (like null) to @Type() with discriminator
• non-exposed type discriminator property when using instanceToPlain with @Exclude()

Added all functional tests for:

• Classes with @Exclude()/@Expose()
• Classes without @Exclude()/@Expose()

Checklist

• the pull request title describes what this PR does (not a vague title like Update index.md)
• the pull request targets the default branch of the repository (develop)
• the code follows the established code style of the repository
  • npm run prettier:check passes
  • npm run lint:check passes
• tests are added for the changes I made (if any source code was modified)
• documentation added or updated
• I have run the project locally and verified that there are no errors

Fixes

fixes #944
fixes #803
fixes #790
fixes #239

[ionutholbia]

Hi all,
I'm waiting for this fix, any ideas when it will be released?

[kol-93]

Hi all, I'm waiting for this fix, any ideas when it will be released?

Many people are waiting for this fix, but authors still don't care about.
So anyone who cares about this fix can use it as dependency like

npm i class-transformer@npm:@kol1993/class-transformer@^0.5.3-alpha.4

[thetilliwilli]

when?

[balkarov]

Hello. I need this fixes too. When will be released?

[Hum4n01d]

Bump! Having issues with this

[kwek20]

Thanks for the PR kol-93
Also needing this. Tagging the last person to merge code in here: @saulotoledo

[jacksrm]

When will this update be released?

[saulotoledo]

@NoNameProvided I've not been active on the project for a while now. Could you take a look at this request or forward it to someone who could look into it?

[nedasoo]

Bump, this is still an ongoing issue

[Sun1ive]

@NoNameProvided this is very needed feature

[kol-93]

@diffy0712 Can somebody review this PR?