Add Support to Inline Fragments

[DimuthuMadushan]

Purpose

Fixes: #1244

Examples

Following query is valid:

query {
    ... on Query {
        profile {
            name
        }
    }
}

on the following service:

import ballerina/graphql;

service graphql:Service on new graphql:Listener(9090) {
    resource function get profile returns Person {
        return { name: "John Doe", age: 20 };
    }
}

type Person record {
    string name;
    int age;
};

Checklist

• Linked to an issue
• Updated the changelog
• Added tests

[codecov]

Codecov Report

Merging #194 (5f2b632) into master (0773c77) will increase coverage by 0.33%.
The diff coverage is 85.10%.

@@             Coverage Diff              @@
##             master     #194      +/-   ##
============================================
+ Coverage     89.48%   89.81%   +0.33%     
  Complexity      196      196              
============================================
  Files            41       41              
  Lines          1654     1689      +35     
  Branches        665      689      +24     
============================================
+ Hits           1480     1517      +37     
+ Misses          158      156       -2     
  Partials         16       16              

Impacted Files	Coverage Δ	Complexity Δ
graphql-ballerina/modules/parser/document_node.bal	76.47% <64.70%> (+8.28%)	0.00 <0.00> (ø)
graphql-ballerina/modules/parser/parser.bal	92.26% <96.42%> (+0.39%)	0.00 <0.00> (ø)
graphql-ballerina/modules/parser/fragment_node.bal	92.00% <100.00%> (+5.04%)	0.00 <0.00> (ø)
graphql-ballerina/validator_visitor.bal	91.17% <0.00%> (+1.47%)	0.00% <0.00%> (ø%)

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[ThisaruGuruge]

Now there are two empty lines?