[rust] Unions named after reserved words result in code that won't compile

[maxburke]

Using flatc with the attached schema definition Schema.fbs.txt

results in a bunch of misgenerated code:

error[E0599]: no method named `type__type` found for reference `&Schema_generated::Field<'a>` in the current scope
    --> /Users/max/target/debug/build/schema-023e5b641b3ecce8/out/flatbuffers/Schema_generated.rs:3813:13
     |
3813 |     if self.type__type() == Type::Null {
     |             ^^^^^^^^^^ help: there is an associated function with a similar name: `type_`

error[E0599]: no method named `type__type` found for reference `&Schema_generated::Field<'a>` in the current scope
    --> /Users/max/target/debug/build/schema-023e5b641b3ecce8/out/flatbuffers/Schema_generated.rs:3828:13
     |
3828 |     if self.type__type() == Type::Int {
     |             ^^^^^^^^^^ help: there is an associated function with a similar name: `type_`

error[E0599]: no method named `type__type` found for reference `&Schema_generated::Field<'a>` in the current scope
    --> /Users/max/target/debug/build/schema-023e5b641b3ecce8/out/flatbuffers/Schema_generated.rs:3843:13
     |
3843 |     if self.type__type() == Type::FloatingPoint {
     |             ^^^^^^^^^^ help: there is an associated function with a similar name: `type_`

error[E0599]: no method named `type__type` found for reference `&Schema_generated::Field<'a>` in the current scope
    --> /Users/max/target/debug/build/schema-023e5b641b3ecce8/out/flatbuffers/Schema_generated.rs:3858:13
     |
3858 |     if self.type__type() == Type::Binary {
     |             ^^^^^^^^^^ help: there is an associated function with a similar name: `type_`

error[E0599]: no method named `type__type` found for reference `&Schema_generated::Field<'a>` in the current scope
    --> /Users/max/target/debug/build/schema-023e5b641b3ecce8/out/flatbuffers/Schema_generated.rs:3873:13
     |
3873 |     if self.type__type() == Type::Utf8 {
     |             ^^^^^^^^^^ help: there is an associated function with a similar name: `type_`

error[E0599]: no method named `type__type` found for reference `&Schema_generated::Field<'a>` in the current scope
    --> /Users/max/target/debug/build/schema-023e5b641b3ecce8/out/flatbuffers/Schema_generated.rs:3888:13
     |
3888 |     if self.type__type() == Type::Bool {
     |             ^^^^^^^^^^ help: there is an associated function with a similar name: `type_`
...

This seems to be a regression of https://github.com/google/flatbuffers/pull/5592

[dbaileychess]

@CasperN

[maxburke]

I've added the failing case to a branch here: https://github.com/urbanlogiq/flatbuffers/tree/flatbuffers-7617