* BUG: Fix PendingDeprecationWarning on _merge_page
* Run CI in this branch

Backport of https://github.com/py-pdf/PyPDF2/pull/898/files

PdfReader: 
* getXmpMetadata / xmpMetadata ➔ xmp_metadata
* get_outlines ➔ _get_outlines (use outlines property instead)

Field attributes:
* additionalActions ➔ additional_actions
* defaultValue ➔ default_value
* mappingName ➔ mapping_name
* altName ➔ alternate_name
* fieldType ➔ field_type

StreamObject: 
* decodedSelf : decoded_self
* flateEncode  ➔ flate_encode

Other:

* Destination: getDestArray ➔ dest_array
* RectangleObject: ensureIsNumber ➔ _ensure_is_number
* TreeObject: addChild / removeChild  ➔ add_child / remove_child
* DecodedStreamObject: getData / setData  ➔ get_data / set_data

See #900

Closes #914

Credits to MasterOdin for:
#915

Deprecations (DEP):
-  PEP8 renaming (#905)

Bug Fixes (BUG):
-  XmpInformation missing method _getText (#917)
-  Fix PendingDeprecationWarning on _merge_page (#904)

Full Changelog: 1.28.2...1.28.3

XmpInformation gave
    TypeError: 'staticmethod' object is not callable

Fix: Move it out of XmpInformation and use the function instead
of the static method

Bug Fixes (BUG):
-  XmpInformation._converter_date was unusable (#921)

Full Changelog: 1.28.3...1.28.4

See #1138 (backport of #1139)

BUG: Add missing deprecated EncodedStreamObject functions (#1140)

Co-authored-by: tst <[email protected]>