Investigate retrieving URIs

[adamretter]

The XQTS causes eXist-db to try and retrieve some resources using its URLSource class.

These resources are not available via the Web. We should investigate whether eXist-db should be retrieving these itself, or whether they should be injected by the XQTS into the XQueryContext as available documents/resources.

Examples of warnings output by eXist-db when running the XQTS:

01 Jul 2022 10:25:51,961 [pool-4-thread-1] WARN  (URLSource.java [getInputStream]:196) - URL 'http://www.w3.org/fots/unparsed-text/non-xml-character.txt' could not be opened: http://www.w3.org/fots/unparsed-text/non-xml-character.txt

01 Jul 2022 10:25:52,224 [pool-4-thread-1] WARN  (URLSource.java [getInputStream]:196) - URL 'http://www.w3.org/fots/unparsed-text/text-plain-utf-16le-bom.txt' could not be opened: http://www.w3.org/fots/unparsed-text/text-plain-utf-16le-bom.txt 
01 Jul 2022 10:25:52,466 [pool-8-thread-1] WARN  (URLSource.java [getInputStream]:196) - URL 'http://www.w3.org/fots/unparsed-text/text-plain-utf-8-invalid.txt' could not be opened: http://www.w3.org/fots/unparsed-text/text-plain-utf-8-invalid.txt 
01 Jul 2022 10:25:52,779 [pool-8-thread-1] WARN  (URLSource.java [getInputStream]:196) - URL 'http://www.w3.org/fots/unparsed-text/text-plain-utf-8-bom-lines-2.txt' could not be opened: http://www.w3.org/fots/unparsed-text/text-plain-utf-8-bom-lines-2.txt 
01 Jul 2022 10:25:53,189 [pool-8-thread-1] WARN  (URLSource.java [getInputStream]:196) - URL 'http://www.w3.org/fots/unparsed-text/text-plain-utf-16be-bom-lines.txt' could not be opened: http://www.w3.org/fots/unparsed-text/text-plain-utf-16be-bom-lines.txt 

Note, it may be that retrieving such resources takes time via Java's URLConnection until a timeout is reached. We should investigate how timeouts are set in eXist-db's URLSource and consider making the timeouts configurable; at which point the XQTS should set a low'ish value for the timeout to reduce its runtime when resources are unavailable.