chore: emit TS declarations

[k-yle]

Currently, this library only publishes the compiled .js files to npm, so there is no easy way for users to access type-defintions like CoverageData:

typescript-coverage-report/src/lib/getCoverage.ts

Lines 13 to 20 in ae28737

	export type CoverageData = {
	fileCounts: FileCount;
	anys: AnyInfo[];
	percentage: number;
	total: number;
	covered: number;
	uncovered: number;
	};

If this MR is accepted, the generated .d.ts files will also be published to npm, which would make it more convinient to access these typedefs