Previously, if ngtsc encountered a VariableDeclaration without an
initializer, it would assume that the variable was undefined, and
return that result.
However, for symbols exported from external modules that resolve to
.d.ts files, variable declarations are of the form:
export declare let varName: Type;
This form also lacks an initializer, but indicates the presence of an
importable symbol which can be referenced. This commit changes the
static resolver to understand variable declarations with the 'declare'
keyword and to generate references when it encounters them.
PR Close#25775
96d6b79ada