feat: add separateReadonlyFromDisabled config option

[kchobantonov]

Allows independent control of readonly and enabled states. Adds READONLY/WRITABLE rule effects. Backward compatible (default: false).

fixes #2479

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[kchobantonov]

@sdirix @lucas-koehler please review - this provides the core and vue-vuetify implementation - the other renderers can be done separately

[coveralls]

coverage: 82.234% (-0.6%) from 82.798%
when pulling f24a9f3 on kchobantonov:separate-readonly-from-disabled
into d3662e2 on eclipsesource:master.

[lucas-koehler]

Hi @kchobantonov , thanks for this contribution ❤️
The changes already look pretty good to me.

I have two points:

1. The calculation !control.enabled || control.readonly is used in many renderers now. Could it make sense to extract a utility for this?
2. We should add unit tests for the following:
   1. evalReadonly() function
   2. hasReadonlyRule() function
   3. isReadonly() function
   4. isInherentlyReadonly() function
   5. The new separateReadonlyFromDisabled config option behavior in isInherentlyEnabled()
   6. The new READONLY and WRITABLE rule effects