test: uniformize VM test helper naming and boolean assertions

[laurentiu021]

Summary

First batch of the modernization+uniformity sweep (test-project uniformity). No production code touched; test: so no release.

Changes

• CreateVm() -> NewVm() in 7 test files (BulkInstaller, ContextMenu, DnsHosts, FileShredder, Performance, Privacy, Uninstaller). The majority of the suite (10 files) already used NewVm(); these 7 were the outliers. Now uniform across all ViewModel tests.
• Assert.Equal(false, result) -> Assert.False((bool)result!) in EqualityConverterTests and IntGreaterThanZeroConverterTests, matching the boolean-assertion style used everywhere else. (The cast is needed because IValueConverter.Convert returns object.)

Verification

• dotnet build (tests project): 0 warnings, 0 errors (TreatWarningsAsErrors=true).
• Pure rename + assertion-style change; no test logic or coverage changed.