Implement concat search pattern semantics for literal, regexp, structural search

Created by: rvantonder

This issue tracks implementing the branching the logic for concat on search patterns. For example, literal search concatenates whitespace, regexp search concatenates (.*)?, etc., and requires testing. Each respective search pattern type (literal, regexp, structural) can be chunked up into 0.5 or 1d tasks.

An example of why this issue is distinctly tracked: consider the literal pattern foo bar baz. It implies foo<single space>bar<single space>baz. Our current implementation treats whitespace sensitively.

In time we may not necessarily want to exactly match whitespace (e.g., to the exact number of spaces), but rather just match the presence of whitespace. There is some existing feedback/request that we be more flexible with handling whitespace in search patterns, and the concat semantics is the place to introduce such a change.