Add pattern property to RegExpFilter to expose already extracted pattern

[mjethani]

Background

The findKeyword method in lib/matcher.js tries to extract the pattern part of the filter text. This is already extracted at the time of creating the Filter object and is available as the value of the internal regexpSource property until the regexp getter is called for the first time. Since the text never really goes away from memory (sliced strings in V8), it makes sense to hold on to it and make it available as a property on the Filter object itself. This way findKeyword can avoid doing all the redundant work.

What to change

Rename RegExpFilter's regexpSource to pattern and make it officially public (whatever this means). In the regexp getter, do not set this property to null. In lib/matcher.js, use the value of this property instead of extracting the same value from the filter text again.

Also delete Filter.regexpRegExp since it is no longer required.

Hints for testers

In general make sure that blocking filters are working correctly:

1. A filter with a pattern like foo*bar should block a URL like https://example.com/foo/a/b/bar?c&d
2. A filter with a regular expression like /foo.*bar/ should block a URL like https://example.com/foo/a/b/bar?c&d

[abpbot]

A commit referencing this issue has landed:
​Issue 6927 - Expose pattern from RegExpFilter

[Ross]

Done. Working as described.

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