Re-encode non-UTF-8-compatible source files.

[dmsnell]

A couple of files in the codebase contain invalid UTF-8. They are encoded as Windows-1252, and if they could be interpreted as such would not be problematic, but as they are, they will be interpreted as UTF-8.

These should be consistently UTF-8 and cleaned up where possible.

Trac ticket: Core-63815

The files in this commit have previously contained text encoded as Windows-1252 (commonly mistaken for latin1/ISO-8859-1), in ways that present invalid UTF-8 bytes.

This commit converts the encodings to UTF-8, which resolves the encoding issues. While the whole-posts document could be argued to be intentionally Windows-1252, there was no obvious evidence that this was more than an historic legacy. The JavaScript file, however, definitely ought to be UTF-8.

[dmsnell]

In 60627:

Convert two source files to UTF-8

The files in this commit have previously contained text encoded as Windows-1252 (commonly mistaken for latin1/ISO-8859-1), in ways that present invalid UTF-8 bytes.

This commit converts the encodings to UTF-8, which resolves the encoding issues. While the whole-posts document could be argued to be intentionally Windows-1252, there was no obvious evidence that this was more than an historic legacy. The JavaScript file, however, definitely ought to be UTF-8.

Developed in ​https://github.com/WordPress/wordpress-develop/pull/9425
Discussed in https://core.trac.wordpress.org/ticket/63815

Props dmsnell, swisspidy.
Fixes #63815.