Fix Post Date Block - Reverts to the default format when the custom date/time format input field is cleared.

[rohitmathur-7]

What?

• In Date Block When custom date/time format input field was cleared then "Default format" setting gets toggled on automatically.
  Fixes Issue: Post Date Block - Reverts to the default format when the custom date/time format input field is cleared.  #64602

Why?

• The input field should remain visible when its value is cleared.

How?

• Added checks so that the input filed remains visible when it is cleared.

Testing Instructions

• Add the Date block to any post/page/template
• Toggle the "Default format" off under Block settings.
• Choose "Custom" from "Choose a format" dropdown.
• Clear the pre-filled text from the format input field - either by selecting all and pressing delete or by deleting the characters one by one.
• When the input field is cleared, now the input filed is still visible.

Screenshots or screencast

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