fix: prevent from "implementation class is not specified" with documentMatcher

[angelozerr]

fix: prevent from "implementation class is not specified" with documentMatcher

When documentMatcher is not declared in languageMapping, fileTypeMapping, etc, the following exception is thrown https://github.com/JetBrains/intellij-community/blob/def6433a5dd9f0a984cbc6e2835d27c97f2cb5f0/platform/core-api/src/com/intellij/serviceContainer/LazyExtensionInstance.java#L55

We catch this method, but it is cleaner to avoid calling getInstance if documentMatcher is not declared.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 15 lines in your changes missing coverage. Please review.

Project coverage is 23.63%. Comparing base (0b8414c) to head (ba149d9).

Files	Patch %	Lines
...sion/FileNamePatternMappingExtensionPointBean.java	0.00%	5 Missing :warning:
...n/extension/FileTypeMappingExtensionPointBean.java	0.00%	5 Missing :warning:
...n/extension/LanguageMappingExtensionPointBean.java	0.00%	5 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #347 +/- ## ========================================== - Coverage 23.67% 23.63% -0.05% ========================================== Files 265 265 Lines 9093 9111 +18 Branches 1243 1243 ========================================== Hits 2153 2153 - Misses 6535 6553 +18 Partials 405 405 ```

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