Add tests for the .editorconfig options that were never set by a test

[meziantou]

What

Ten documented .editorconfig options were not set by any test in the test assembly. Each now has a test in both directions: the default behavior, and the behavior once the option is set to the other value.

Option	Test file
MA0003.excluded_methods	NamedParameterAnalyzerTests.cs
MA0011.exclude_tostring_methods	UseIFormatProviderAnalyzerTests.cs
MA0045.enable_sqlite_special_cases, MA0045.enable_db_special_cases	DoNotUseBlockingCallInAsyncContextAnalyzerTests.cs
MA0053.class_with_virtual_member_should_be_sealed	ClassMustBeSealedAnalyzerTests.cs
MA0075.exclude_tostring_methods, MA0075.consider_nullable_types, MA0076.consider_nullable_types	DoNotUseImplicitCultureSensitiveToStringAnalyzerTests.cs
MA0104.only_consider_public_symbols	DotNotUseNameFromBCLAnalyzerTests.cs
MA0139.allow_non_constant_formats	LoggerParameterTypeAnalyzer_SerilogTests.cs

Tests only — no analyzer or documentation changes. dotnet run --project src/DocumentationGenerator exits 0 with no markdown changes.

Why

These options are the documented escape hatch when a rule misfires. With no test setting the key, a rename, a mis-parse, or a flipped default fails silently and only surfaces in users' own repositories.

Two cases were sharper than the rest:

• MA0053 defines a hidden legacy key with a typo (class_with_virtual_member_shoud_be_sealed) alongside the documented class_with_virtual_member_should_be_sealed. Both existing tests set only the misspelled legacy key, so the spelling users are told to write in docs/Rules/MA0053.md had no coverage at all.
• MA0045 and MA0139 each duplicate a key owned by a sibling rule (MA0042 and MA0124). Only the sibling's copy was covered.

Notes for the reviewer

• Where a documented key is paired with another one, the tests also pin the precedence rather than just the on/off behavior: MA0045.enable_*_special_cases overrides the MA0042 key (in both directions), and the documented MA0053 spelling overrides the hidden misspelled one.
• MA0045.enable_db_special_cases and MA0045.enable_sqlite_special_cases default to true, so the meaningful direction — turning the DB/SQLite special-casing off — had never been taken by a test.
• main was merged in to resolve a conflict in NamedParameterAnalyzerTests.cs, where both sides added a test at the same place around a shared body. Both are kept: this branch's two MA0003.excluded_methods tests, and Int32_ExcludedMethodWithEmptyRegex_ShouldReportDiagnostic from main.

Verification

Full suite after merging main: 19668 passed, 0 failed, 0 skipped across roslyn4.8 / 4.14 / 5.0 / 5.6 / 5.9.