Definitions: Only emit links for canonical type mentions

[pavgust]

In 1.17, we could emit many logically indistinguishable type mentions for the same type/location where a file was processed in many different contexts. On very large projects, this can lead to an inflation in the number of definitions links that are emitted.

With this change, we'll pick a canonical type mention for each location/type pair, and only emit link information for that.

[aibaars]

This line seems unrelated.

[pavgust]

You're right. It's morally part of #223, but I had somehow neglected to stage it. @jbj, for info -- let's keep this hotfix patch together, as it's what I tested.

[jbj]

Test failure in ql/cpp/ql/test/query-tests/definitions/definitions.qlref due to the suppression of ClassTemplateInstantiation:

11:47:29 Diff:
11:47:29 --- expected
11:47:29 +++ actual
11:47:29 @@ -17,7 +17,6 @@
11:47:29  | class.cpp:16:16:16:22 | mention of myClass | class.cpp:2:7:2:13 | myClass | T |
11:47:29  | class.cpp:26:29:26:32 | _val | class.cpp:26:17:26:20 | _val | V |
11:47:29  | class.cpp:35:1:35:14 | mention of myIntContainer | class.cpp:9:7:9:20 | myIntContainer | T |
11:47:29 -| class.cpp:36:1:36:12 | mention of myTContainer<char> | class.cpp:23:7:23:18 | myTContainer<char> | T |
11:47:29  | class.cpp:38:30:38:36 | mention of myClass | class.cpp:2:7:2:13 | myClass | T |
11:47:29  | class.cpp:45:2:45:8 | mention of myClass | class.cpp:2:7:2:13 | myClass | T |
11:47:29  | class.cpp:51:2:51:8 | mention of myClass | class.cpp:2:7:2:13 | myClass | T |
11:47:29 @@ -88,7 +87,6 @@
11:47:29  | type_mentions.cpp:18:8:18:15 | mention of MyClass2<1> | type_mentions.cpp:14:7:14:14 | MyClass2<1> | T |
11:47:29  | type_mentions.cpp:18:24:18:31 | mention of MyClass1 | type_mentions.cpp:1:7:1:14 | MyClass1 | T |
11:47:29  | type_mentions.cpp:27:3:27:11 | mention of MyStruct1 | type_mentions.cpp:21:10:21:18 | MyStruct1 | T |
11:47:29 -| type_mentions.cpp:35:1:35:14 | mention of BinaryTemplate<MyClass1, MyStruct1> | type_mentions.cpp:31:7:31:20 | BinaryTemplate<MyClass1, MyStruct1> | T |
11:47:29  | type_mentions.cpp:35:16:35:23 | mention of MyClass1 | type_mentions.cpp:1:7:1:14 | MyClass1 | T |
11:47:29  | type_mentions.cpp:35:40:35:48 | mention of MyStruct1 | type_mentions.cpp:21:10:21:18 | MyStruct1 | T |
11:47:29  | type_mentions.cpp:39:24:39:32 | mention of MyStruct1 | type_mentions.cpp:21:10:21:18 | MyStruct1 | T |

@pavgust, these look like valid rows that are removed and are not replaced by anything else.

[pavgust]

As discussed, we'll handle this differently.