fix: export cont REQUEST_METHOD_MAP from router-method-factory

[Makkalay]

It is useful piece of code for create custom adapter

PR Checklist

Please check if your PR fulfills the following requirements:

• [x ] The commit message follows our guidelines: https://github.com/nestjs/nest/blob/master/CONTRIBUTING.md
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• [ x] Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Other... Please describe:

What is the current behavior?

const REQUEST_METHOD_MAP { *** }

Issue Number: N/A

What is the new behavior?

export const REQUEST_METHOD_MAP { *** }

Does this PR introduce a breaking change?

• Yes
• [x ] No

Other information

For example people do that
[type HttpMethods =] = *** (https://github.com/seidelmartin/nest-koa-adapter/blob/d83478e55351be128762836a9cffff0e12b5c234/src/KoaAdapter.ts#L22)

but can use REQUEST_METHOD_MAP

I need for example something like:

m !== REQUEST_METHOD_MAP[RequestMethod.ALL]
          ? REQUEST_METHOD_MAP[m] as Method : undefined

[coveralls]

Pull Request Test Coverage Report for Build ede61a1a-12fa-4e14-a246-7aa375263bd8

Details

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 91.912%

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Totals
Change from base Build e25bebae-20b1-4a99-b89e-69eb0e86d7a3:	0.0%
Covered Lines:	6818
Relevant Lines:	7418

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💛 - Coveralls