feat!: change `$t` overloaded signature for Legacy API mode

feature (has breaking change)

In Vue I18n v9, it has a different interface from the Composition API mode and Legacy API mode of the $t overloaded signature.

Especially, $t signature in Legacy API mode has fewer overloaded signatures than in Composition API mode, as shown below:

`$t` overloaded signatures	Legacy API v9	Legacy API v10	Composition API v9 & v10
`$t(key: Path): TranslateResult;`	✅	✅	✅
`$t(key: Path, locale: Locale): TranslateResult;`	✅	-	-
`$t(key: Path, locale: Locale, list: unknown[]): TranslateResult;`	✅	-	-
`$t(key: Path, locale: Locale, named: NamedValue): TranslateResult;`	✅	-	-
`$t(key: Path, plural: number): TranslateResult;`	-	✅	✅
`$t(key: Path, plural: number, options: TranslateOptions): TranslateResult;`	-	✅	✅
`$t(key: Path, defaultMsg: string): TranslateResult;`	-	✅	✅
`$t(key: Path, defaultMsg: string, options: TranslateOptions): TranslateResult;`	-	✅	✅
`$t(key: Path, list: unknown[]): TranslateResult;`	✅	✅	✅
`$t(key: Path, list: unknown[], plural: number): TranslateResult;`	-	✅	✅
`$t(key: Path, list: unknown[], defaultMsg: string): TranslateResult;`	-	✅	✅
`$t(key: Path, list: unknown[], options: TranslateOptions): TranslateResult;`	-	✅	✅
`$t(key: Path, named: Record<string, unknown>): TranslateResult;`	✅	✅	✅
`$t(key: Path, named: NamedValue, plural: number): TranslateResult;`	-	✅	✅
`$t(key: Path, named: NamedValue, defaultMsg: string): TranslateResult;`	-	✅	✅
`$t(key: Path, named: NamedValue, options: TranslateOptions): TranslateResult;`	-	✅	✅

Starting from v10, Legacy API mode can use the same $t overload signature as Composition API mode.

Reason: After that migration, when migrating to Composition API mode, we sometimes fall into a pitfall due to the different signature of $t.

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