Remove ^L characters hidden randomly in the code. Not those used in text files as delimiters.

While working on a tool that processes Erlang code and testing it against this repo,
I found out about those little sneaky 0xff. I thought it may be of help to other
people build such tools to remove non-conforming-to-standard characters.
Merge branch 'fenollp/treewide_remove_unexpected_0xff/OTP-11323' into maint

* fenollp/treewide_remove_unexpected_0xff/OTP-11323:
  Remove ^L characters hidden randomly in the code. Not those used in text files as delimiters.
xmerl: Add tests for XPath queries that resolve the context namespace

Ensures that both the original namespace prefix and a namespace prefix
provided to the xmlContext will both return the same sets of nodes.
xmerl: Look up unknown prefixes in xmlContext when matching attributes

The core use case is a query where the original prefix in the scanned
document is unknown (or varying).  For example:

  xmerl_xpath:scan("//@ns:name", Doc, [{namespace, [{"ns", Uri}]}])

Previously, this would only return a result if the namespace prefix
was an exact match.
xmerl: Use context namespace declarations to resolve prefix node tests

Previously, a match would not be found if the namespace prefix in the
XPath query was not contained in the original document.  This allows
the `namespace' option to provide a prefix that will be resolved to a
namespace URI.

See Section 2.3 of the XPath 1.0 specification for the behaviour of
'NCName:*' node tests.
Avoid serialization on code_server in xmerl:export()

The inheritance mechanism in xmerl used to use 'catch apply(M,F,Args)' to
try different modules M until one was found that had a function F/A.
However, when M:F/A does not exist, apply/3 will trap to
error_handler:undefined_function/3, which will call code:ensure_loaded(M),
making a synchronous request to the code server process. If many processes
tried to use xmerl:export() concurrently, they would get serialized waiting
for the code server process. This patch uses erlang:function_exported/3
instead to check if M:F/A exists. If M exists, it should already have been
loaded at that point due to the inheritance checking in the
xmerl:callbacks/1 function.
Merge branch 'richcarl/xmerl-avoid-code-server-serialization/OTP-11463' into maint

* richcarl/xmerl-avoid-code-server-serialization/OTP-11463:
  Avoid serialization on code_server in xmerl:export()
Prepare release