add getter to event req & res object in default handler.

[KensukeTakahara]

This fixies #2327.

The reason for this bug is the same as for #2344.
When useV2Handler: true set in serverless.yml, this problem was not solved.

I Implemented getter function in default handler.

[slsnextbot]

Handler Size Report

There are changes to handler sizes. Please review.

Base Handler Sizes (kB) (commit 07b0685)

{
    "Lambda": {
        "Default Lambda": {
            "Standard": 1524,
            "Minified": 668
        },
        "Image Lambda": {
            "Standard": 1488,
            "Minified": 800
        }
    },
    "Lambda@Edge": {
        "Default Lambda": {
            "Standard": 1534,
            "Minified": 673
        },
        "Default Lambda V2": {
            "Standard": 1526,
            "Minified": 670
        },
        "API Lambda": {
            "Standard": 634,
            "Minified": 318
        },
        "Image Lambda": {
            "Standard": 1496,
            "Minified": 805
        },
        "Regeneration Lambda": {
            "Standard": 1187,
            "Minified": 546
        },
        "Regeneration Lambda V2": {
            "Standard": 1253,
            "Minified": 573
        }
    }
}

New Handler Sizes (kB) (commit 9e3f79f)

{
    "Lambda": {
        "Default Lambda": {
            "Standard": 1524,
            "Minified": 668
        },
        "Image Lambda": {
            "Standard": 1488,
            "Minified": 800
        }
    },
    "Lambda@Edge": {
        "Default Lambda": {
            "Standard": 1534,
            "Minified": 674
        },
        "Default Lambda V2": {
            "Standard": 1526,
            "Minified": 670
        },
        "API Lambda": {
            "Standard": 634,
            "Minified": 318
        },
        "Image Lambda": {
            "Standard": 1496,
            "Minified": 805
        },
        "Regeneration Lambda": {
            "Standard": 1187,
            "Minified": 546
        },
        "Regeneration Lambda V2": {
            "Standard": 1253,
            "Minified": 573
        }
    }
}

[codecov]

Codecov Report

Merging #2381 (9e3f79f) into master (07b0685) will increase coverage by 0.16%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2381      +/-   ##
==========================================
+ Coverage   83.60%   83.77%   +0.16%     
==========================================
  Files         102      102              
  Lines        3691     3697       +6     
  Branches     1184     1186       +2     
==========================================
+ Hits         3086     3097      +11     
+ Misses        593      588       -5     
  Partials       12       12              

Impacted Files	Coverage Δ
packages/libs/core/src/handle/default.ts	97.61% <100.00%> (+11.50%)	⬆️
packages/libs/core/src/route/page.ts	78.87% <0.00%> (+1.40%)	⬆️

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