Revise & standardise clipboard handling

[delphidabbler]

PasHi & PasHiGUI use different methods of accessing the clipboard.

Reading code is different in each program: PasHi uses low level API calls while PasHiGUI uses OLE.

Writing code uses the low level API again in PasHi, while PasHiGUI uses the VCL Clipboard object.

This is a mess thats crying out for shared code. It would be much better to standardise on one method of access, preferably the OLE object.

Maybe a new TClipboardAdapter class is called for to get the OLE clipboard object and use code derived from PasHiGUI's TDataObjectAdapter class to help handle the IDataObject instances obtained from the clipboard.

See Src/GUI/UDataObjectAdapter.pas for TDataObjectAdapter.

Originally posted by @delphidabbler in #39 (comment)

[delphidabbler]

This issue is an expansion of issue #39, and replaces it.

Issue #39 has been closed, but the comments in it are valuable and reference various source code files that may need attention.

So, review the comments in issue #39 while implementing this issue.

[delphidabbler]

There are two criteria that both PasHi and PasHiGUI must follow when handling text on the clipboard:

1. Text must always be written to the clipboard in Unicode format. In addition Text may be written in the default ANSI encoding ⭐, if appropriate.
2. When reading text from the clipboard, an attempt must first be made to read in Unicode format. If that format is not available then ANSI format text ⭐ may be read.

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⭐ See comments in issue #39 about determining whether Windows ever creates the ANSI clipboard without also making available a Unicode format version.

[delphidabbler]

Given that PasHiGUI also accepts file drops / pastes, should PasHi also accept files copied to the clipboard?

[delphidabbler]

Given that PasHiGUI also accepts file drops / pastes, should PasHi also accept files copied to the clipboard?

This proposal now has its own issue - #74.