nimsuggest: fix and re-enable old tests (#16401)

A number of nimsuggest tests were disabled for various reasons, sometimes due
to brittleness. These tests have been fixed where needed and most have are now
enabled -- details below. The updates are meant to provide better regression
coverage for future nimsuggest improvements. To avoid brittleness some tests
were refactored.

Impact:
* test coverage has now increased
* faster execution of the test suite
* tests are less likely to break due to stdlib changes

Re-enabled Test & Test Description:
* `tchk1.nim`: check (chk) via nimsuggest works at end of file
* `tdot4.nim`: prioritize already used completion
* `tinclude.nim`: definition lookup (def) with includes
* `tstrutils.nim` -> `tdef2.nim`: test template definition lookup (def)
* `tsug_regression.nim`: regression test for [nimsuggest #52](https://github.com/nim-lang/nimsuggest/issues/52)
* `ttemplate_highlight.nim`: per the file name
* `twithin_macro_prefix.nim`: suggest within a macro with a prefix

Tests Not Re-Enabled:
* `twithin_macro.nim` still disabled as it doesn't provide a good test signal
* EPC highlight tests remain disabled -- requires out of scope tester changes

Additional Notes:
* todos added in comments for follow-up work

nimsuggest/tests/tdot4.nim

@@ -1,17 +1,21 @@
-discard """
-disabled:true
-$nimsuggest --tester --maxresults:2 $file
->sug $1
-sug;;skProc;;tdot4.main;;proc (inp: string): string;;$file;;10;;5;;"";;100;;None
-sug;;skProc;;strutils.replace;;proc (s: string, sub: string, by: string): string{.noSideEffect, gcsafe, locks: 0.};;$lib/pure/strutils.nim;;1506;;5;;"Replaces `sub` in `s` by the string `by`.";;100;;None
-"""
+# Test that already used suggestions are prioritized
 
-import strutils
+from system import string, echo
+import fixtures/mstrutils
 
 proc main(inp: string): string =
   # use replace here and see if it occurs in the result, it should gain
   # priority:
   result = inp.replace(" ", "a").replace("b", "c")
 
-
 echo "string literal here".#[!]#
+
+# priority still tested, but limit results to avoid failures from other output
+discard """
+$nimsuggest --tester --maxresults:2 $file
+>sug $1
+sug;;skProc;;tdot4.main;;proc (inp: string): string;;$file;;6;;5;;"";;100;;None
+sug;;skFunc;;mstrutils.replace;;proc (s: string, sub: string, by: string): string{.noSideEffect, gcsafe, locks: 0.};;*fixtures/mstrutils.nim;;9;;5;;"this is a test version of strutils.replace, it simply returns `by`";;100;;None
+"""
+
+# TODO - determine appropriate behaviour for further suggest output and test it