Support legacy problem matchers

[tolusha]

Description

There is a task which comes from quarkus extension [1] and it is invalid due to the error regarding problemMatcher:

Incorrect type. Expected "string".
Value is not accepted. Valid values: "$clangTidyMatcher", "$eslint-compact", "$eslint-stylish", "$go", "$gulp-tsc", "$jshint", "$jshint-stylish", "$lessCompile", "$msCompile".(1)

     {
         "label": "quarkus:dev",
         "type": "shell",
         "command": "./mvnw quarkus:dev ",
         "windows": {
            "command": ".\\mvnw.cmd quarkus:dev "
         },
         "isBackground": true,
         "problemMatcher": [
            {
               "pattern": [
                  {
                     "regexp": "\\b\\B",
                     "file": 1,
                     "location": 2,
                     "message": 3
                  }
               ],
               "background": {
                  "activeOnStart": true,
                  "beginsPattern": "^.*Scanning for projects...*",
                  "endsPattern": "^.*Quarkus .* started in .*\\. Listening on:*"
               }
            }
         ]
      }

It seems Theia problemMatcher scheme is different from VS Code one [3]

[1] https://github.com/redhat-developer/vscode-quarkus
[2] https://github.com/eclipse-theia/theia/blame/master/packages/task/src/browser/task-schema-updater.ts#L215
[3] https://github.com/Microsoft/vscode/blob/master/src/vs/workbench/contrib/tasks/common/jsonSchemaCommon.ts#L37

[tsmaeder]

@tolusha what's the difference?

[tolusha]

type: 'array',
					items: {
						anyOf: [
							{
								type: 'string',
							},
							Schemas.LegacyProblemMatcher
						]
					}

vs

type: 'array',
            description: 'Name(s) of the problem matcher(s) to parse the output of the task',
            items: {
                type: 'string',
                enum: problemMatcherNames
            }

[elaihau]

the current schema is

const problemMatcher = {
    oneOf: [
        {
            type: 'string',
            description: 'Name of the problem matcher to parse the output of the task',
            enum: problemMatcherNames
        },
        {
            type: 'object',
            description: 'User defined problem matcher(s) to parse the output of the task',
        },
        {
            type: 'array',
            description: 'Name(s) of the problem matcher(s) to parse the output of the task',
            items: {
                type: 'string',
                enum: problemMatcherNames
            }
        }
    ]
};

and therefore "an array of objects" is not supported.

I can added the support.

[tolusha]

@elaihau
It will be nice!