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/tinclude.nim

@@ -1,8 +1,19 @@
+# import that has an include, def calls must work into and out of includes
+import fixtures/minclude_import
+
+proc go() =
+  discard create().say()
+
+go()
+
 discard """
-disabled:true
-$nimsuggest --tester compiler/nim.nim
->def compiler/semexprs.nim:25:50
-def;;skType;;ast.PSym;;PSym;;*ast.nim;;707;;2;;"";;100
->def compiler/semexprs.nim:25:50
-def;;skType;;ast.PSym;;PSym;;*ast.nim;;707;;2;;"";;100
+$nimsuggest --tester $file
+>def $path/tinclude.nim:5:14
+def;;skProc;;minclude_import.create;;proc (greeting: string, subject: string): Greet{.noSideEffect, gcsafe, locks: 0.};;*fixtures/minclude_include.nim;;3;;5;;"";;100
+>def $path/fixtures/minclude_include.nim:3:71
+def;;skType;;minclude_types.Greet;;Greet;;*fixtures/minclude_types.nim;;4;;2;;"";;100
+>def $path/fixtures/minclude_include.nim:3:71
+def;;skType;;minclude_types.Greet;;Greet;;*fixtures/minclude_types.nim;;4;;2;;"";;100
 """
+
+# TODO test/fix if the first `def` is not first or repeated we get no results